feat: remove deprecated functions

feat: add as_something functions for convenience

.circleci/config.yml

@@ -0,0 +1,59 @@
+version: 2.1
+
+jobs:
+  test_suite:
+    environment:
+      - GOPATH: /home/circleci/go
+    docker:
+      - image: circleci/golang:1.9
+    steps:
+      - checkout
+      - run:
+          command: |
+              g++ --version
+              cd tests/
+              g++ -std=c++11 -O2 -Wall -Wextra -Werror -I../ check_toml_test.cpp -o check_toml_test
+              go get github.com/BurntSushi/toml-test
+              $GOPATH/bin/toml-test ./check_toml_test
+  output_result:
+    docker:
+      - image: circleci/buildpack-deps:bionic
+    steps:
+      - checkout
+      - run:
+          command: |
+              g++ --version
+              cd tests/
+              g++ -std=c++11 -O2 -Wall -Wextra -Werror -I../ check.cpp -o check
+              git clone https://github.com/BurntSushi/toml-test.git
+              cp check toml-test/tests/invalid
+              cp check toml-test/tests/valid
+              cd toml-test/tests/invalid
+              for f in $(ls ./*.toml);
+                do echo "==> ${f}";
+                cat ${f};
+                echo "---------------------------------------";
+                ./check ${f} invalid;
+                if [ $? -ne 0 ] ; then
+                  exit 1
+                fi
+                echo "=======================================";
+              done
+              cd ../valid
+              for f in $(ls ./*.toml);
+                do echo "==> ${f}";
+                cat ${f};
+                echo "---------------------------------------";
+                ./check ${f} valid;
+                if [ $? -ne 0 ] ; then
+                  exit 1
+                fi
+                echo "=======================================";
+              done
+
+workflows:
+  version: 2.1
+  test:
+    jobs:
+      - test_suite
+      - output_result

.travis.yml

@@ -5,7 +5,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: gcc
-    env: COMPILER="g++-5"
+    env: COMPILER="g++-5" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -16,7 +16,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: gcc
-    env: COMPILER="g++-6"
+    env: COMPILER="g++-6" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -27,7 +27,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: gcc
-    env: COMPILER="g++-7"
+    env: COMPILER="g++-7" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -38,7 +38,18 @@ matrix:
   - os: linux
     language: cpp
     compiler: gcc
-    env: COMPILER="g++-8"
+    env: COMPILER="g++-8" CXX_STANDARD=11
+    addons:
+      apt:
+        sources:
+        - ubuntu-toolchain-r-test
+        packages:
+        - g++-8
+        - libboost-all-dev
+  - os: linux
+    language: cpp
+    compiler: gcc
+    env: COMPILER="g++-8" CXX_STANDARD=17
     addons:
       apt:
         sources:
@@ -49,7 +60,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: clang
-    env: COMPILER="clang++-3.7"
+    env: COMPILER="clang++-3.7" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -61,7 +72,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: clang
-    env: COMPILER="clang++-4.0"
+    env: COMPILER="clang++-4.0" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -73,7 +84,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: clang
-    env: COMPILER="clang++-5.0"
+    env: COMPILER="clang++-5.0" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -85,7 +96,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: clang
-    env: COMPILER="clang++-6.0"
+    env: COMPILER="clang++-6.0" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -97,7 +108,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: clang
-    env: COMPILER="clang++-7"
+    env: COMPILER="clang++-7" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -109,7 +120,7 @@ matrix:
   - os: linux
     language: cpp
     compiler: clang
-    env: COMPILER="clang++-8"
+    env: COMPILER="clang++-8" CXX_STANDARD=11
     addons:
       apt:
         sources:
@@ -118,14 +129,38 @@ matrix:
         packages:
         - clang-8
         - libboost-all-dev
+  - os: linux
+    language: cpp
+    compiler: clang
+    env: COMPILER="clang++-8" CXX_STANDARD=17
+    addons:
+      apt:
+        sources:
+        - ubuntu-toolchain-r-test
+        - llvm-toolchain-trusty-8
+        packages:
+        - clang-8
+        - g++-8
+        - libboost-all-dev
   - os: osx
     language: cpp
     compiler: clang
+    env: CXX_STANDARD=11
 
 script:
+- |
+  if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
+    mkdir -p cmake
+    travis_retry wget "https://cmake.org/files/v3.11/cmake-3.11.2-Linux-x86_64.tar.gz"
+    tar xf cmake-3.11.2-Linux-x86_64.tar.gz -C cmake --strip-components=1
+    export PATH=${TRAVIS_BUILD_DIR}/cmake/bin:${PATH}
+  else
+    brew upgrade cmake
+  fi
+- cmake --version
 - mkdir build
 - cd build
 - git clone https://github.com/toml-lang/toml.git
-- cmake -DCMAKE_CXX_COMPILER=$COMPILER ..
+- cmake -DCMAKE_CXX_COMPILER=$COMPILER -DCMAKE_CXX_STANDARD=$CXX_STANDARD ..
 - make
 - ctest --output-on-failure

CMakeLists.txt

@@ -4,7 +4,10 @@ project(toml11)
 
 include(CheckCXXCompilerFlag)
 if("${CMAKE_VERSION}" VERSION_GREATER 3.1)
+    set(CMAKE_CXX_EXTENSIONS OFF)
+    if(NOT DEFINED CMAKE_CXX_STANDARD)
         set(CMAKE_CXX_STANDARD 11)
+    endif()
     set(CXX_STANDARD_REQUIRED ON)
 else()
     # Manually check for C++11 compiler flag.

README.md

@@ -1,74 +1,126 @@
 toml11
 ======
 
-[![Build Status](https://travis-ci.org/ToruNiina/toml11.svg?branch=master)](https://travis-ci.org/ToruNiina/toml11)
+[![Build Status on TravisCI](https://travis-ci.org/ToruNiina/toml11.svg?branch=master)](https://travis-ci.org/ToruNiina/toml11)
-[![Build status](https://ci.appveyor.com/api/projects/status/m2n08a926asvg5mg/branch/master?svg=true)](https://ci.appveyor.com/project/ToruNiina/toml11/branch/master)
+[![Build status on Appveyor](https://ci.appveyor.com/api/projects/status/m2n08a926asvg5mg/branch/master?svg=true)](https://ci.appveyor.com/project/ToruNiina/toml11/branch/master)
+[![Build status on CircleCI](https://circleci.com/gh/ToruNiina/toml11/tree/master.svg?style=svg)](https://circleci.com/gh/ToruNiina/toml11/tree/master)
 [![Version](https://img.shields.io/github/release/ToruNiina/toml11.svg?style=flat)](https://github.com/ToruNiina/toml11/releases)
 [![License](https://img.shields.io/github/license/ToruNiina/toml11.svg?style=flat)](LICENSE)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.1209136.svg)](https://doi.org/10.5281/zenodo.1209136)
 
-C++11 header-only toml parser/encoder depending only on C++ standard library.
+toml11 is a C++11 header-only toml parser/encoder depending only on C++ standard library.
 
 compatible to the latest version of
 [TOML v0.5.0](https://github.com/toml-lang/toml/blob/master/versions/en/toml-v0.5.0.md)
 after version 2.0.0.
 
-Are you looking for pre-C++11 compatible toml parser?
+It passes [the language agnostic test suite for TOML parsers by BurntSushi](https://github.com/BurntSushi/toml-test).
-Try [Boost.toml](https://github.com/ToruNiina/Boost.toml)!
+Not only the test suite itself, a TOML reader/encoder also runs on [CircleCI](https://circleci.com/gh/ToruNiina/toml11).
-It has almost the same functionality as this library and works with C++98 & Boost.
+You can see the error messages about invalid files and serialization results of valid files at
+[CircleCI](https://circleci.com/gh/ToruNiina/toml11).
 
-## How to use
+## Example
 
-## Installation
+```cpp
+#include <toml11/toml.hpp>
+#include <iostream>
+
+int main()
+{
+    const auto data  = toml::parse("example.toml");
+
+    // title = "an example toml file"
+    std::string title = toml::get<std::string>(data.at("title"));
+    std::cout << "the title is " << title << std::endl;
+
+    // nums = [1, 2, 3, 4, 5]
+    std::vector<int> nums  = toml::get<std::vector<int>>(data.at("nums"));
+    std::cout << "the length of `nums` is" << nums.size() << std::endl;
+
+    return 0;
+}
+```
+
+## Table of Contents
+
+- [Integration](#integration)
+- [Decoding a toml file](#decoding-a-toml-file)
+  - [In the case of syntax error](#in-the-case-of-syntax-error)
+- [Getting a toml value](#getting-a-toml-value)
+  - [In the case of type error](#in-the-case-of-type-error)
+- [Getting an array](#getting-an-array)
+- [Getting a table](#getting-a-table)
+  - [Dotted keys](#dotted-keys)
+- [Getting an array of tables](#getting-an-array-of-tables)
+- [Cost of conversion](#cost-of-conversion)
+- [Getting datetime and its variants](#getting-datetime-and-its-variants)
+- [Getting with a fallback](#getting-with-a-fallback)
+- [Expecting conversion](#expecting-conversion)
+- [Finding a value from a table](#finding-a-value-from-a-table)
+- [Checking value type](#checking-value-type)
+- [Visiting a toml::value](#visiting-a-tomlvalue)
+- [TOML literal](#toml-literal)
+- [Conversion between toml value and arbitrary types](#conversion-between-toml-value-and-arbitrary-types)
+- [Invalid UTF-8 Codepoints](#invalid-utf-8-codepoints)
+- [Formatting user-defined error messages](#formatting-user-defined-error-messages)
+- [Getting comments related to a value](#getting-comments)
+- [Serializing TOML data](#serializing-toml-data)
+- [Underlying types](#underlying-types)
+- [Running Tests](#running-tests)
+- [Contributors](#contributors)
+- [Licensing Terms](#licensing-terms)
+
+## Integration
 
 Just include the file after adding it to the include path.
 
 ```cpp
 #include <toml11/toml.hpp> // that's all! now you can use it.
+#include <iostream>
 
 int main()
 {
     const auto data  = toml::parse("example.toml");
     const auto title = toml::get<std::string>(data.at("title"));
     std::cout << "the title is " << title << std::endl;
+    return 0;
 }
 ```
 
-### Decoding toml file
+## Decoding a toml file
 
-The only thing you have to do is to pass a filename to the `toml::parse` function.
+To parse a toml file, the only thing you have to do is
+to pass a filename to the `toml::parse` function.
 
 ```cpp
 const std::string fname("sample.toml");
 const toml::table data = toml::parse(fname);
 ```
 
-In the case of file open error, it will throw `std::runtime_error`.
+If it encounters a file open error, it will throw `std::runtime_error`.
 
-You can also pass a `stream` to the  `toml::parse` function after checking the status.
+You can also pass a `std::istream` to the  `toml::parse` function.
-
+To show a filename in an error message, it is recommended to pass the filename
-Note that on __Windows OS__, stream that is opened as text-mode automatically converts
+with the stream.
-CRLF ("\r\n") into LF ("\n") and this leads inconsistency between file size and
-the contents that would be read. This causes weird error. To use a file stream
-with `toml::parse`, don't forget to pass binary mode flag when you open the
-stream.
 
 ```cpp
 std::ifstream ifs("sample.toml", std::ios_base::binary);
 assert(ifs.good());
-const auto data = toml::parse(ifs /*, "filename" (optional)*/);
+const auto data = toml::parse(ifs, /*optional*/ "sample.toml");
 ```
 
-To show a better error message, it is recommended to pass a filename with `istream`.
+Note that on Windows, if a file is opened in text-mode, CRLF ("\r\n") will
-See also [in the case of syntax error](#in-the-case-of-syntax-error)
+automatically be converted to LF ("\n") and this causes inconsistency between
-and [passing invalid type to toml::get](#passing-invalid-type-to-tomlget).
+file size and the contents that would be read. This causes weird error.
+To use a file stream with `toml::parse` on Windows, don't forget to open it
+in binary mode.
 
 ### In the case of syntax error
 
 If there is a syntax error in a toml file, `toml::parse` will throw `toml::syntax_error`.
 
-toml11 now has clean and informative error messages inspired by Rust and
+toml11 has clean and informative error messages inspired by Rust and
-it looks like the following (comment after hash sign are actually not shown).
+it looks like the following.
 
 ```console
 terminate called after throwing an instance of 'toml::syntax_error'
@@ -78,8 +130,8 @@ terminate called after throwing an instance of 'toml::syntax_error'
    |        ^------ expected newline, but got '='.        # error reason
 ```
 
-If you (mistakenly) duplicate tables and got an error, you may want to see
+If you (mistakenly) duplicate tables and got an error, it is helpful to see
-where the other is. toml11 shows both at the same time.
+where they are. toml11 shows both at the same time like the following.
 
 ```console
 terminate called after throwing an instance of 'toml::syntax_error'
@@ -93,15 +145,16 @@ terminate called after throwing an instance of 'toml::syntax_error'
 ```
 
 Since the error message generation is generally a difficult task, the current
-status is not ideal. toml11 needs your help. If you encounter a weird error message,
+status is not ideal. If you encounter a weird error message, please let us know
-please let us know and contribute to improve the quality!
+and contribute to improve the quality!
 
-### Getting a toml value
+## Getting a toml value
 
 After parsing successfully, you can obtain the values from the result of
-`toml::parse` (here, `data`) using `toml::get` function.
+`toml::parse` using `toml::get` function.
 
 ```toml
+# sample.toml
 answer  = 42
 pi      = 3.14
 numbers = [1,2,3]
@@ -111,6 +164,7 @@ key = "value"
 ```
 
 ``` cpp
+const auto data      = toml::parse("sample.toml");
 const auto answer    = toml::get<std::int64_t    >(data.at("answer"));
 const auto pi        = toml::get<double          >(data.at("pi"));
 const auto numbers   = toml::get<std::vector<int>>(data.at("numbers"));
@@ -120,20 +174,30 @@ const auto key       = toml::get<std::string>( tab.at("key"));
 ```
 
 When you pass an exact TOML type that does not require type conversion,
-`toml::get` returns also a reference through which you can modify the content.
+`toml::get` returns a reference through which you can modify the content.
 
 ```cpp
-toml::get<toml::integer>(data["answer"]) = 6 * 9;
+auto  data   = toml::parse("sample.toml");
+auto& answer = toml::get<toml::integer>(data["answer"]);     // get reference
+answer = 6 * 9;                                              // write to data.answer
 std::cout << toml::get<int>(data.at("answer")) << std::endl; // 54
 ```
 
 If the specified type requires conversion, you can't take a reference to the value.
 See also [underlying types](#underlying-types).
 
-#### Passing invalid type to toml::get
+NOTE: To enable to get a reference, conversions between Float and Integer are not supported.
 
-If you choose the invalid type, `toml::type_error` will be thrown.
+After C++17, you can use `std::string_view` to get a string from a `toml::value`.
-Similar to the `syntax_error`, toml11 also displays informative error messages.
+
+```cpp
+const auto sv = toml::get<std::string_view>(tab.at("key"));
+```
+
+### In the case of type error
+
+If you pass an invalid type to `toml::get`, `toml::type_error` will be thrown.
+Similar to the case of syntax error, toml11 also displays clean error messages.
 The error message when you choose `int` to get `string` value would be like this.
 
 ```console
@@ -144,15 +208,21 @@ terminate called after throwing an instance of 'toml::type_error'
    |         ~~~~~~~~~~~~~~ the actual type is string
 ```
 
-NOTE: In order to show this kind of error message, all the toml values have 1
+NOTE: In order to show this kind of error message, all the toml values have
-`shared_ptr` that points the corresponding byte sequence and 2 iterators that point the range.
+pointers to represent its range in a file. The entire contents of a file is
-It is recommended to destruct all the `toml::value` classes after configuring your application to save memory resources.
+shared by `toml::value`s and remains on the heap memory. It is recommended to
+destruct all the `toml::value` classes after configuring your application
+if you have a large TOML file compared to the memory resource.
 
-### Getting arrays
+## Getting an array
 
-You can set any kind of `container` class to obtain a `toml::array` except for `map`-like classes.
+You can get any kind of `container` class from a `toml::array`
+except for `map`-like classes.
 
 ``` cpp
+// # sample.toml
+// numbers = [1,2,3]
+
 const auto vc  = toml::get<std::vector<int>  >(data.at("numbers"));
 const auto ls  = toml::get<std::list<int>    >(data.at("numbers"));
 const auto dq  = toml::get<std::deque<int>   >(data.at("numbers"));
@@ -161,16 +231,16 @@ const auto ar  = toml::get<std::array<int, 3>>(data.at("numbers"));
 // it will throw toml::type_error because std::array is not resizable.
 ```
 
-Surprisingly, you can also get a `toml::array` as `std::pair` and `std::tuple.`
+Surprisingly, you can also get `std::pair`s and `std::tuple`s from `toml::array`.
 
 ```cpp
 const auto tp = toml::get<std::tuple<short, int, unsigned int>>(data.at("numbers"));
 ```
 
-The case when you need this functionality is to get an array of arrays.
+This functionality is helpful when you have the following toml file.
 
 ```toml
-aofa = [[1,2,3], ["foo", "bar", "baz"]] # toml allows this
+array_of_arrays = [[1, 2, 3], ["foo", "bar", "baz"]] # toml allows this
 ```
 
 What is the corresponding C++ type? Obviously, it is a `std::pair` of `std::vector`s.
@@ -178,21 +248,21 @@ What is the corresponding C++ type? Obviously, it is a `std::pair` of `std::vect
 ```cpp
 const auto aofa = toml::get<
     std::pair<std::vector<int>, std::vector<std::string>>
-    >(data.at("aofa"));
+    >(data.at("array_of_arrays"));
 ```
 
-If you don't know what the type is inside the array, you can use `toml::array`,
+If you don't know the type of the elements, you can use `toml::array`,
 which is a `std::vector` of `toml::value`, instead.
 
 ```cpp
-const auto aofa  = toml::get<toml::array>(data.at("aofa"));
+const auto aofa  = toml::get<toml::array>(data.at("array_of_arrays"));
-const auto first = toml::get<toml::array>(aofa.at(0));
+const auto first = toml::get<std::vector<int>>(aofa.at(0));
 ```
 
 See also [expecting conversion](#expecting-conversion)
 and [checking-value-type](#checking-value-type).
 
-### Getting tables
+## Getting a table
 
 `toml::table` is a key component of this library, which is an alias of
 a `std::unordered_map` from `toml::key (a.k.a. std::string)` to `toml::value`.
@@ -219,12 +289,13 @@ key2 = "bar" # toml String
 ```
 
 ```cpp
+const auto data = toml::parse("sample.toml");
 const auto tab = toml::get<std::map<std::string, std::string>>(data.at("tab"));
 std::cout << tab["key1"] << std::endl; // foo
 std::cout << tab["key2"] << std::endl; // bar
 ```
 
-### Dotted keys
+## Dotted keys
 
 TOML v0.5.0 has a new feature named "dotted keys".
 You can chain keys to represent the structure of the data.
@@ -249,41 +320,49 @@ const auto physical = toml::get<toml::table>(data.at("physical"));
 const auto color    = toml::get<std::string>(physical.at("color"));
 ```
 
-### An array of tables
+## Getting an array of tables
 
 An array of tables is just an array of tables.
 You can get it completely in the same way as the other arrays and tables.
 
 ```toml
-array_of_inline_table = [{key = "value1"}, {key = "value2"}, {key = "value3"}]
+# sample.toml
+array_of_inline_tables = [{key = "value1"}, {key = "value2"}, {key = "value3"}]
 
-[[array_of_table]]
+[[array_of_tables]]
 key = "value4"
-[[array_of_table]]
+[[array_of_tables]]
 key = "value5"
-[[array_of_table]]
+[[array_of_tables]]
 key = "value6"
 ```
 
 ```cpp
-const auto aot1 = toml::get<std::vector<toml::table>>(data.at("array_of_inline_table"));
+const auto data = toml::parse("sample.toml");
-const auto aot2 = toml::get<std::vector<toml::table>>(data.at("array_of_table"));
+const auto aot1 = toml::get<std::vector<toml::table>>(data.at("array_of_inline_tables"));
+const auto aot2 = toml::get<std::vector<toml::table>>(data.at("array_of_tables"));
 ```
 
-### Cost of conversion
+## Cost of conversion
 
 Although `toml::get` is convenient, it has additional copy-cost because
 it copies data contained in `toml::value` to the user-specified type.
-Of course in some case this overhead is not ignorable.
+Of course in some cases this overhead is not ignorable.
 
-By passing the exact types, `toml::get` returns reference that has nealy zero overhead.
+```cpp
+// the following code constructs a std::vector.
+// it requires heap allocation for vector and element conversion.
+const auto array = toml::get<std::vector<int>>(data.at("foo"));
+```
+
+By passing the exact types, `toml::get` returns reference that has no overhead.
 
 ``` cpp
 const auto& tab     = toml::get<toml::array>(data.at("tab"));
 const auto& numbers = toml::get<toml::table>(data.at("numbers"));
 ```
 
-Unfortunately, in this case you need to call `toml::get` each time you access to
+In this case you need to call `toml::get` each time you access to
 the element of `toml::array` because `toml::array` is an array of `toml::value`.
 
 ```cpp
@@ -292,34 +371,61 @@ const auto& num1 = toml::get<toml::integer>(numbers.at(1));
 const auto& num2 = toml::get<toml::integer>(numbers.at(2));
 ```
 
-### Datetime and its variants
+## Getting datetime and its variants
 
 TOML v0.5.0 has 4 different datetime objects, `local_date`, `local_time`,
-`local_datetime`, and `offset_datetime`. With toml11, you can convert `local_time`
+`local_datetime`, and `offset_datetime`.
-to your favorite `std::chrono::duration` and others to `std::chrono::system_clock::time_point`.
+
+Since `local_date`, `local_datetime`, and `offset_datetime` represent a time
+point, you can convert them to `std::chrono::system_clock::time_point`.
+
+Contrary, `local_time` does not represents a time point because they lack a
+date information, but it can be converted to `std::chrono::duration` that
+represents a duration from the beginning of the day, `00:00:00.000`.
 
 ```toml
-time = 12:30:00
 date = 2018-12-23
+time = 12:30:00
+l_dt = 2018-12-23T12:30:00
+o_dt = 2018-12-23T12:30:00+09:30
 ```
 
 ```cpp
-const auto dur = toml::get<std::chrono::minutes>(data.at("time")); // 12 * 60 + 30 min
+const auto data = toml::parse("sample.toml");
-const auto tp  = toml::get<std::chrono::system_clock::time_point>(data.at("date"));
+
+const auto date = toml::get<std::chrono::system_clock::time_point>(data.at("date"));
+const auto l_dt = toml::get<std::chrono::system_clock::time_point>(data.at("l_dt"));
+const auto o_dt = toml::get<std::chrono::system_clock::time_point>(data.at("o_dt"));
+
+const auto time = toml::get<std::chrono::minutes>(data.at("time")); // 12 * 60 + 30 min
 ```
 
-### Getting with a fallback
+toml11 contains datetime as its own struct.
+You can see the definitions in [toml/datetime.hpp](toml/datetime.hpp).
+
+## Getting with a fallback
 
 `toml::get_or` returns a default value if `toml::get<T>` failed.
 
 ```cpp
-toml::table data; // empty table!
+toml::value v("foo"); // v contains String
-const auto value = toml::get_or(data, "key", 42); // value => int 42.
+const int value = toml::get_or(v, 42); // conversion fails. it returns 42.
 ```
 
-`toml::get_or` automatically deduces what type you want to get from the default value you passed.
+`toml::get_or` automatically deduces what type you want to get from
+the default value you passed.
 
-### Expecting conversion
+To get a reference through this function, take care about the default value.
+
+```cpp
+toml::value v("foo"); // v contains String
+toml::integer& i = toml::get_or(v, 42); // does not work because binding `42`
+                                        // to `integer&` is invalid
+toml::integer opt = 42;
+toml::integer& i = toml::get_or(v, opt); // this works.
+```
+
+## Expecting conversion
 
 By using `toml::expect`, you will get your expected value or an error message
 without throwing `toml::type_error`.
@@ -343,7 +449,7 @@ const auto value = toml::expect<int>(data.at("number"))
     }).unwrap_or(/*default value =*/ 3.14);
 ```
 
-### Finding value from table
+## Finding a value from a table
 
 toml11 provides utility function to find a value from `toml::table`.
 Of course, you can do this in your own way with `toml::get` because
@@ -354,7 +460,7 @@ const auto data = toml::parse("example.toml");
 const auto num  = toml::find<int>(data, "num", /*for err msg*/"example.toml");
 ```
 
-If the value does not exist, it throws `std::out_of_range` with informative error message.
+If the value does not exist, it throws `std::out_of_range` with an error message.
 
 ```console
 terminate called after throwing an instance of 'std::out_of_range'
@@ -373,7 +479,8 @@ const auto num  = toml::find<int>(data.at("table"), "num");
 ```
 
 In this case, because the value `data.at("table")` knows the locatoin of itself,
-you don't need to pass where you find the value. `toml::find` will show you a great error message.
+you don't need to pass where you find the value.
+`toml::find` will show you an error message including table location.
 
 ```console
 terminate called after throwing an instance of 'std::out_of_range'
@@ -385,9 +492,45 @@ terminate called after throwing an instance of 'std::out_of_range'
 
 If it's not a `toml::table`, the same error as "invalid type" would be thrown.
 
-### Checking value type
+There is another utility function, `toml::find_or`.
+It is almost same as `toml::find`, but returns a default value if the value is
+not found or has a different type, like `toml::get_or`.
 
-When you don't know the exact type of toml-value, you can get `enum` type from `toml::value`.
+```cpp
+const auto data = toml::parse("example.toml");
+const auto num  = toml::find_or(data.at("table"), "num", 42);
+```
+
+## Checking value type
+
+You can check what type of value does `toml::value` contains by `is_*` function.
+
+```cpp
+toml::value v = /* ... */;
+if(v.is_integer())
+{
+    std::cout << "value is an integer" << std::endl;
+}
+```
+
+The complete list of the functions is below.
+
+```cpp
+const toml::value v(/*...*/);
+v.is_boolean();
+v.is_integer();
+v.is_float();
+v.is_string();
+v.is_offset_datetime();
+v.is_local_datetime();
+v.is_local_date();
+v.is_local_time();
+v.is_array();
+v.is_table();
+v.is_uninitialized();
+```
+
+Also, you can get `enum class` value from `toml::value`.
 
 ```cpp
 switch(data.at("something").type())
@@ -400,32 +543,49 @@ switch(data.at("something").type())
 }
 ```
 
-### Fill only the matched value
+The complete list of the `enum`s can be found in the section
+[underlying types](#underlying-types).
 
-The more sophisticated way is using `toml::from_toml` and `std::tie`.
+The `enum`s can be used as a parameter of `toml::value::is` function like the following.
 
 ```cpp
-toml::table data{{"something", toml::value("foo")}};
+toml::value v = /* ... */;
-int         i = 0;
+if(v.is(toml::value_t::Boolean)) // ...
-double      d = 0.;
-std::string s;
-toml::from_toml(std::tie(i, d, s), data.at("something"));
-std::cout << i << ", " << d << ", " << s << std::endl; // 0, 0, foo
 ```
 
-Here, only matched value will be filled. The others are left intact after calling `from_toml`.
+## Casting value
-It should be noted that `toml::from_toml` returns as usual even if there are no matched type.
 
-`from_toml` can be used also for single type. 
+So far, `toml::get` is introduced, but if you don't need any type conversion,
+`as_*` is simpler to use.
 
 ```cpp
-int i = 0;
+toml::value v = /* ... */;
-toml::from_toml(i, data.at("something"));
+if(v.is_integer() && v.as_integer() == 42)
+{
+    std::cout << "value is 42" << std::endl;
+}
 ```
 
-### visiting toml::value
+The complete list of the functions is below.
 
-TOML v2.1.0+ provides `toml::visit` to apply a function to `toml::value` in the
+```cpp
+const toml::value v(/*...*/);
+v.as_boolean();
+v.as_integer();
+v.as_float();
+v.as_string();
+v.as_offset_datetime();
+v.as_local_datetime();
+v.as_local_date();
+v.as_local_time();
+v.as_array();
+v.as_table();
+v.as_uninitialized();
+```
+
+## Visiting a toml::value
+
+toml11 provides `toml::visit` to apply a function to `toml::value` in the
 same way as `std::variant`.
 
 ```cpp
@@ -439,29 +599,223 @@ The function object that would be passed to `toml::visit` must be able to
 recieve all the possible TOML types. Also, the result types should be the same
 each other.
 
-### Sanitizing UTF-8 codepoints
+## TOML literal
 
-toml11 shows warning if a value of an escape sequence used
+toml11 supports `"..."_toml` literal.
-to represent unicode character exceeds the unicode range.
+It accept both a bare value and a file content.
 
-```console
+```cpp
-[warning] input codepoint (0011FFFF) is too large to decode as a unicode character. The result may not be able to render to your screen.
+using namespace toml::literals::toml_literals;
- --> example.toml
+
- 3 | exceeds_unicode = "\U0011FFFF example"
+// `_toml` can convert a bare value without key
-   |                     ~~~~~~~~~ should be in [0x00..0x10FFFF]
+const toml::value v = u8"0xDEADBEEF"_toml;
+// v is an Integer value containing 0xDEADBEEF.
+
+// raw string literal (`R"(...)"` is useful for this purpose)
+const toml::value t = u8R"(
+    title = "this is TOML literal"
+    [table]
+    key = "value"
+)"_toml;
+// the literal will be parsed and the result will be contained in t
 ```
 
-Also, toml11 throws `std::domain_error` if the code point exceeds the range that can be represented by utf-8.
+The literal function is defined in the same way as the standard library literals
+such as `std::literals::string_literals::operator""s`.
 
-```console
+```cpp
-terminate called after throwing an instance of 'std::range_error'
+namespace toml
-  what():  [error] input codepoint (0020FFFF) is too large to encode as utf-8.
+{
- --> example.toml
+inline namespace literals
- 3 | exceeds_utf8    = "\U0020FFFF example"
+{
-   |                     ~~~~~~~~~ should be in [0x00..0x10FFFF]
+inline namespace toml_literals
+{
+toml::value operator""_toml(const char* str, std::size_t len);
+
+} // toml_literals
+} // literals
+} // toml
 ```
 
-### Formatting your error
+Access to the operator can be gained with `using namespace toml::literals;`,
+`using namespace toml::toml_literals`, and `using namespace toml::literals::toml_literals`.
+
+Note that a key that is composed only of digits is allowed in TOML.
+And, unlike the file parser, toml-literal allows a bare value without a key.
+Thus it is difficult to distinguish arrays having integers and definitions of
+tables that are named as digits.
+Currently, literal `[1]` becomes a table named "1".
+To ensure a literal to be considered as an array with one element, you need to
+add a comma after the first element (like `[1,]`).
+
+```cpp
+"[1,2,3]"_toml;   // This is an array
+"[table]"_toml;   // This is a table that has an empty table named "table" inside.
+"[[1,2,3]]"_toml; // This is an array of arrays
+"[[table]]"_toml; // This is a table that has an array of tables inside.
+
+"[[1]]"_toml;     // This literal is ambiguous.
+                  // Currently, it becomes a table that has array of table "1".
+"1 = [{}]"_toml;  // This is a table that has an array of table named 1.
+"[[1,]]"_toml;    // This is an array of arrays.
+"[[1],]"_toml;    // ditto.
+```
+
+## Conversion between toml value and arbitrary types
+
+You can also use `toml::get` and other related functions with the types you defined
+after you implement some stuff.
+
+```cpp
+namespace ext
+{
+struct foo
+{
+    int         a;
+    double      b;
+    std::string c;
+};
+} // ext
+
+const auto data = toml::parse("example.toml");
+
+const foo f = toml::get<ext::foo>(data.at("foo"));
+```
+
+There are 2 ways to use `toml::get` with the types that you defined.
+
+The first one is to implement `from_toml(const toml::value&)` member function.
+
+```cpp
+namespace ext
+{
+struct foo
+{
+    int         a;
+    double      b;
+    std::string c;
+
+    void from_toml(const toml::value& v)
+    {
+        this->a = toml::find<int        >(v, "a");
+        this->b = toml::find<double     >(v, "b");
+        this->c = toml::find<std::string>(v, "c");
+        return;
+    }
+};
+} // ext
+```
+
+In this way, because `toml::get` first constructs `foo` without arguments,
+the type should be default-constructible.
+
+The second is to implement specialization of `toml::from` for your type.
+
+```cpp
+namespace ext
+{
+struct foo
+{
+    int         a;
+    double      b;
+    std::string c;
+};
+} // ext
+
+namespace toml
+{
+template<>
+struct from<ext::foo>
+{
+    ext::foo from_toml(const toml::value& v)
+    {
+        ext::foo f;
+        f.a = toml::find<int        >(v, "a");
+        f.b = toml::find<double     >(v, "b");
+        f.c = toml::find<std::string>(v, "c");
+        return f;
+    }
+};
+} // toml
+```
+
+In this way, since the conversion function is defined outside of the class,
+you can add conversion between `toml::value` and classes defined in another library.
+
+Note that you cannot implement both of the functions because the overload
+resolution of `toml::get` will be ambiguous.
+
+----
+
+The opposite direction is also supported in a similar way. You can directly
+pass your type to `toml::value`'s constructor by introducing `into_toml` or
+`toml::into<T>`.
+
+```cpp
+namespace ext
+{
+struct foo
+{
+    int         a;
+    double      b;
+    std::string c;
+
+    toml::table into_toml() const // you need to mark it const.
+    {
+        return toml::table{{"a", this->a}, {"b", this->b}, {"c", this->c}};
+    }
+};
+} // ext
+
+ext::foo    f{42, 3.14, "foobar"};
+toml::value v(f);
+```
+
+The definition of `toml::into<T>` is similar to `toml::from<T>`.
+
+```cpp
+namespace ext
+{
+struct foo
+{
+    int         a;
+    double      b;
+    std::string c;
+};
+} // ext
+
+namespace toml
+{
+template<>
+struct into<ext::foo>
+{
+    toml::table into_toml(const ext::foo& f)
+    {
+        return toml::table{{"a", f.a}, {"b", f.b}, {"c", f.c}};
+    }
+};
+} // toml
+
+ext::foo    f{42, 3.14, "foobar"};
+toml::value v(f);
+```
+
+Any type that can be converted to `toml::value`, e.g. `toml::table`, `toml::array`,
+is okay to return from `into_toml`.
+
+## Invalid UTF-8 codepoints
+
+toml11 throws `syntax_error` if a value of an escape sequence
+representing unicode character is not a valid UTF-8 codepoint.
+
+```console
+  what():  [error] toml::read_utf8_codepoint: input codepoint is too large.
+ --> utf8.toml
+ 1 | exceeds_unicode = "\U0011FFFF example"
+   |                              ^--------- should be in [0x00..0x10FFFF]
+```
+
+## Formatting user-defined error messages
 
 When you encounter an error after you read the toml value, you may want to
 show the error with the value.
@@ -514,22 +868,65 @@ you will get an error message like this.
    |       ~~ maximum number here
 ```
 
-### Serializing TOML data
+## Getting comments
 
-toml11 v2.1.0 enables you to serialize data into toml format.
+Since toml11 keeps a file data until all the values are destructed, you can
+also extract a comment related to a value by calling `toml::value::comment()`.
+
+If there is a comment just after a value (within the same line), you can get
+the specific comment by `toml::value::comment_inline()`.
+
+If there are comments just before a value (without any newline between them),
+you can get the comments by `toml::value::comment_before()`.
+
+`toml::value::comment()` returns the results of both functions after
+concatenating them.
+
+```toml
+a = 42 # comment for a.
+
+# comment for b.
+# this is also a comment for b.
+b = "foo"
+
+c = [ # comment for c.
+    3.14, # this is not a comment for c, but for 3.14.
+] # this is also a comment for c.
+```
+
+```cpp
+// "# comment for a."
+const std::string com1 = toml::find(data, "a").comment();
+
+// "# comment for b."
+const std::string com2 = toml::find(data, "b").comment();
+
+// "# comment for c.\n# this is also a comment for c."
+const std::string com3 = toml::find(data, "c").comment();
+
+// "# this is not a comment for c, but for 3.14."
+const std::string com3 = toml::find<toml::array>(data, "c").front().comment();
+```
+
+Note that once a data in a value is modified, the related file region
+information would be deleted. Thus after modifying a data, you cannot find any
+comments.
+
+Also note that currently it does not support any way to set a comment to a value.
+And currently, serializer does not take comments into account.
+
+## Serializing TOML data
+
+toml11 (after v2.1.0) enables you to serialize data into toml format.
 
 ```cpp
 const auto data = toml::table{{"foo", 42}, {"bar", "baz"}};
-
-const std::string serial = toml::format(data);
-// serial == "{bar=\"baz\",foo=42}"
-
 std::cout << data << std::endl;
 // bar = "baz"
 // foo = 42
 ```
 
-toml11 automatically makes a tiny table and array inline.
+toml11 automatically makes a small table and small array inline.
 You can specify the width to make them inline by `std::setw` for streams.
 
 ```cpp
@@ -572,23 +969,8 @@ It is recommended to set width before printing data. Some I/O functions changes
 width to 0, and it makes all the stuff (including `toml::array`) multiline.
 The resulting files becomes too long.
 
-`toml::format` receives optional second argument to set the width.
-By default, it is 80.
-
-```cpp
-const auto data = toml::table{
-    {"qux", toml::table{{"foo", 42}, {"bar", "baz"}}}
-};
-
-const std::string serial = toml::format(data, /*width = */ 0);
-// [qux]
-// bar = "baz"
-// foo = 42
-```
-
 To control the precision of floating point numbers, you need to pass
-`std::setprecision` to stream or pass `int` to the optional third argument of
+`std::setprecision` to stream.
-`toml::format` (by default, it is `std::numeric_limits<double>::max_digit10`).
 
 ```cpp
 const auto data = toml::table{
@@ -601,8 +983,32 @@ std::cout << std::setprecision(17) << data << std::endl;
 std::cout << std::setprecision( 7) << data << std::endl;
 // e = 2.718282
 // pi = 3.141593
+```
 
-const std::string serial = toml::format(data, /*width = */ 0, /*prec = */ 17);
+There is another way to format toml values, `toml::format()`.
+It returns `std::string` that represents a value.
+
+```cpp
+const toml::value v{{"a", 42}};
+const std::string fmt = toml::format(v);
+// a = 42
+```
+
+Note that since `toml::format` formats a value, the resulting string may lack
+the key value.
+
+```cpp
+const toml::value v{3.14};
+const std::string fmt = toml::format(v);
+// 3.14
+```
+
+To control the width and precision, `toml::format` receives optional second and
+third arguments to set them. By default, the witdh is 80 and the precision is
+`std::numeric_limits<double>::max_digit10`.
+
+```cpp
+const auto serial = toml::format(data, /*width = */ 0, /*prec = */ 17);
 ```
 
 ## Underlying types
@@ -618,7 +1024,7 @@ The toml types (can be used as `toml::*` in this library) and corresponding `enu
 | LocalDate      | `toml::local_date`                           | `toml::value_t::LocalDate`      |
 | LocalTime      | `toml::local_time`                           | `toml::value_t::LocalTime`      |
 | LocalDatetime  | `toml::local_datetime`                       | `toml::value_t::LocalDatetime`  |
-| OffsetDatetime | `toml::offset_datetime`                      | `toml::value_t::offsetDatetime` |
+| OffsetDatetime | `toml::offset_datetime`                      | `toml::value_t::OffsetDatetime` |
 | Array          | `std::vector<toml::value>`                   | `toml::value_t::Array`          |
 | Table          | `std::unordered_map<toml::key, toml::value>` | `toml::value_t::Table`          |
 
@@ -633,21 +1039,40 @@ not capable of representing a Local Time independent from a specific day.
 
 It is recommended to get `Datetime`s as `std::chrono` classes through `toml::get`.
 
+## Running Tests
+
+To run test codes, you need to clone toml-lang/toml repository under `build/` directory
+because some of the test codes read a file in the repository.
+
+```sh
+$ mkdir build
+$ cd build
+$ git clone https://github.com/toml-lang/toml.git
+$ cmake ..
+$ make
+$ make test
+```
+
+To run the language agnostic test suite, you need to compile
+`tests/check_toml_test.cpp` and pass it to the tester.
+
 ## Contributors
 
-I thank the contributor for providing great feature to this repository.
+I appreciate the help of the contributors who introduced the great feature to this library.
 
 - Guillaume Fraux (@Luthaf)
   - Windows support and CI on Appvayor
   - Intel Compiler support
 - Quentin Khan (@xaxousis)
   - Found & Fixed a bug around ODR
-  - Improved error message to show the location where the parser fails
+  - Improved error messages for invaild keys to show the location where the parser fails
+- Petr Beneš (@wbenny)
+  - Fixed warnings on MSVC
 
 ## Licensing terms
 
 This product is licensed under the terms of the [MIT License](LICENSE).
 
-- Copyright (c) 2017 Toru Niina
+- Copyright (c) 2017-2019 Toru Niina
 
 All rights reserved.

tests/CMakeLists.txt

@@ -20,15 +20,17 @@ set(TEST_NAMES
     test_parse_inline_table
     test_parse_key
     test_parse_table_key
+    test_literals
+    test_comments
     test_get
     test_get_related_func
-    test_to_toml
     test_from_toml
     test_parse_file
     test_serialize_file
     test_parse_unicode
     test_error_detection
     test_format_error
+    test_extended_conversions
 )
 
 CHECK_CXX_COMPILER_FLAG("-Wall" COMPILER_SUPPORTS_WALL)
@@ -98,3 +100,8 @@ foreach(TEST_NAME ${TEST_NAMES})
         )
     endif()
 endforeach(TEST_NAME)
+
+# this test is to check it compiles. it will not run
+add_executable(test_multiple_translation_unit
+               test_multiple_translation_unit_1.cpp
+               test_multiple_translation_unit_2.cpp)

tests/check.cpp

@@ -0,0 +1,41 @@
+#include "toml.hpp"
+#include <iostream>
+#include <iomanip>
+
+int main(int argc, char **argv)
+{
+    if(argc != 3)
+    {
+        std::cerr << "usage: ./check [filename] [valid|invalid]" << std::endl;
+        return 1;
+    }
+
+    const std::string file_kind(argv[2]);
+
+    try
+    {
+        const auto data = toml::parse(argv[1]);
+        std::cout << std::setprecision(16) << std::setw(80) << data;
+        if(file_kind == "valid")
+        {
+            return 0;
+        }
+        else
+        {
+            return 1;
+        }
+    }
+    catch(const toml::syntax_error& err)
+    {
+        std::cout << "what(): " << err.what() << std::endl;
+        if(file_kind == "invalid")
+        {
+            return 0;
+        }
+        else
+        {
+            return 1;
+        }
+    }
+    return 127;
+}

tests/check_toml_test.cpp

@@ -0,0 +1,142 @@
+#include "toml.hpp"
+#include <iostream>
+#include <iomanip>
+
+struct json_serializer
+{
+    void operator()(toml::boolean v)
+    {
+        std::cout << "{\"type\":\"bool\",\"value\":\"" << toml::value(v) << "\"}";
+        return ;
+    }
+    void operator()(toml::integer v)
+    {
+        std::cout << "{\"type\":\"integer\",\"value\":\"" << toml::value(v) << "\"}";
+        return ;
+    }
+    void operator()(toml::floating v)
+    {
+        std::cout << "{\"type\":\"float\",\"value\":\"" << toml::value(v) << "\"}";
+        return ;
+    }
+    void operator()(const toml::string& v)
+    {
+        // since toml11 automatically convert string to multiline string that is
+        // valid only in TOML, we need to format the string to make it valid in
+        // JSON.
+        std::cout << "{\"type\":\"string\",\"value\":\""
+                  << this->escape_string(v.str) << "\"}";
+        return ;
+    }
+    void operator()(const toml::local_time& v)
+    {
+        std::cout << "{\"type\":\"local_time\",\"value\":\"" << toml::value(v) << "\"}";
+        return ;
+    }
+    void operator()(const toml::local_date& v)
+    {
+        std::cout << "{\"type\":\"local_date\",\"value\":\"" << toml::value(v) << "\"}";
+        return ;
+    }
+    void operator()(const toml::local_datetime& v)
+    {
+        std::cout << "{\"type\":\"local_datetime\",\"value\":\"" << toml::value(v) << "\"}";
+        return ;
+    }
+    void operator()(const toml::offset_datetime& v)
+    {
+        std::cout << "{\"type\":\"datetime\",\"value\":\"" << toml::value(v) << "\"}";
+        return ;
+    }
+    void operator()(const toml::array& v)
+    {
+        if(!v.empty() && v.front().is_table())
+        {
+            std::cout << '[';
+            bool is_first = true;
+            for(const auto& elem : v)
+            {
+                if(!is_first) {std::cout << ", ";}
+                is_first = false;
+                toml::visit(*this, elem);
+            }
+            std::cout << ']';
+        }
+        else
+        {
+            std::cout << "{\"type\":\"array\",\"value\":[";
+            bool is_first = true;
+            for(const auto& elem : v)
+            {
+                if(!is_first) {std::cout << ", ";}
+                is_first = false;
+                toml::visit(*this, elem);
+            }
+            std::cout << "]}";
+        }
+        return ;
+    }
+    void operator()(const toml::table& v)
+    {
+        std::cout << '{';
+        bool is_first = true;
+        for(const auto& elem : v)
+        {
+            if(!is_first) {std::cout << ", ";}
+            is_first = false;
+            std::cout << toml::format(toml::string(elem.first),
+                                      std::numeric_limits<std::size_t>::max());
+            std::cout << ':';
+            toml::visit(*this, elem.second);
+        }
+        std::cout << '}';
+        return ;
+    }
+
+    std::string escape_string(const std::string& s) const
+    {
+        std::string retval;
+        for(const char c : s)
+        {
+            switch(c)
+            {
+                case '\\': {retval += "\\\\"; break;}
+                case '\"': {retval += "\\\""; break;}
+                case '\b': {retval += "\\b";  break;}
+                case '\t': {retval += "\\t";  break;}
+                case '\f': {retval += "\\f";  break;}
+                case '\n': {retval += "\\n";  break;}
+                case '\r': {retval += "\\r";  break;}
+                default  : {retval += c;      break;}
+            }
+        }
+        return retval;
+    }
+};
+
+int main()
+{
+    try
+    {
+        std::vector<char> buf;
+        std::cin.peek();
+        while(!std::cin.eof())
+        {
+            buf.push_back(std::cin.get());
+            std::cin.peek();
+        }
+        std::string bufstr(buf.begin(), buf.end());
+
+        std::istringstream ss(bufstr);
+
+        const auto data = toml::parse(ss);
+        std::cout << std::setprecision(std::numeric_limits<double>::max_digits10);
+        toml::visit(json_serializer(), data);
+        return 0;
+    }
+    catch(const toml::syntax_error& err)
+    {
+        std::cout << "what(): " << err.what() << std::endl;
+        return 1;
+    }
+}

tests/test_comments.cpp

@@ -0,0 +1,125 @@
+#define BOOST_TEST_MODULE "test_comments"
+#ifdef UNITTEST_FRAMEWORK_LIBRARY_EXIST
+#include <boost/test/unit_test.hpp>
+#else
+#define BOOST_TEST_NO_LIB
+#include <boost/test/included/unit_test.hpp>
+#endif
+
+#include <toml.hpp>
+
+BOOST_AUTO_TEST_CASE(test_comment_before)
+{
+    using namespace toml::literals::toml_literals;
+    {
+        const toml::value v = u8R"(
+            # comment for a.
+            a = 42
+            # comment for b.
+            b = "baz"
+        )"_toml;
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_before(), u8"# comment for a.");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_before(), u8"# comment for b.");
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_inline(), "");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_inline(), "");
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment(), u8"# comment for a.");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment(), u8"# comment for b.");
+    }
+
+    {
+        const toml::value v = u8R"(
+            # comment for a.
+            # another comment for a.
+            a = 42
+            # comment for b.
+            # also comment for b.
+            b = "baz"
+        )"_toml;
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_before(), u8R"(# comment for a.
+# another comment for a.)");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_before(), u8R"(# comment for b.
+# also comment for b.)");
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_inline(), u8"");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_inline(), u8"");
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment(), u8R"(# comment for a.
+# another comment for a.)");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment(), u8R"(# comment for b.
+# also comment for b.)");
+    }
+}
+
+BOOST_AUTO_TEST_CASE(test_comment_inline)
+{
+    using namespace toml::literals::toml_literals;
+    {
+        const toml::value v = u8R"(
+            a = 42    # comment for a.
+            b = "baz" # comment for b.
+        )"_toml;
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_before(), "");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_before(), "");
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_inline(), u8"# comment for a.");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_inline(), u8"# comment for b.");
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment(), u8"# comment for a.");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment(), u8"# comment for b.");
+    }
+    {
+        const toml::value v = u8R"(
+            a = [    # comment for a.
+                42,
+            ] # this also.
+            b = [ # comment for b.
+                "bar",
+            ]
+            c = [
+                3.14, # this is not a comment for c, but 3.14.
+            ] # comment for c.
+        )"_toml;
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_before(), "");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_before(), "");
+        BOOST_CHECK_EQUAL(toml::find(v, "c").comment_before(), "");
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_inline(), u8R"(# comment for a.
+# this also.)");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_inline(), u8"# comment for b.");
+        BOOST_CHECK_EQUAL(toml::find(v, "c").comment_inline(), u8"# comment for c.");
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment(),  u8R"(# comment for a.
+# this also.)");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment(), u8"# comment for b.");
+        BOOST_CHECK_EQUAL(toml::find(v, "c").comment(), u8"# comment for c.");
+
+        const auto& c0 = toml::find<toml::array>(v, "c").at(0);
+        BOOST_CHECK_EQUAL(c0.comment(), u8"# this is not a comment for c, but 3.14.");
+    }
+}
+
+BOOST_AUTO_TEST_CASE(test_comment_both)
+{
+    using namespace toml::literals::toml_literals;
+    {
+        const toml::value v = u8R"(
+            # comment for a.
+            a = 42 # inline comment for a.
+            # comment for b.
+            b = "baz" # inline comment for b.
+        )"_toml;
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_before(), "# comment for a.");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_before(), "# comment for b.");
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment_inline(), "# inline comment for a.");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment_inline(), "# inline comment for b.");
+
+        BOOST_CHECK_EQUAL(toml::find(v, "a").comment(), u8R"(# comment for a.
+# inline comment for a.)");
+        BOOST_CHECK_EQUAL(toml::find(v, "b").comment(), u8R"(# comment for b.
+# inline comment for b.)");
+    }
+}

tests/test_extended_conversions.cpp

@@ -0,0 +1,116 @@
+#define BOOST_TEST_MODULE "test_extended_conversions"
+#ifdef UNITTEST_FRAMEWORK_LIBRARY_EXIST
+#include <boost/test/unit_test.hpp>
+#else
+#define BOOST_TEST_NO_LIB
+#include <boost/test/included/unit_test.hpp>
+#endif
+#include <toml.hpp>
+
+namespace extlib
+{
+struct foo
+{
+    int a;
+    std::string b;
+};
+struct bar
+{
+    int a;
+    std::string b;
+
+    void from_toml(const toml::value& v)
+    {
+        this->a = toml::find<int>(v, "a");
+        this->b = toml::find<std::string>(v, "b");
+        return ;
+    }
+
+    toml::table into_toml() const
+    {
+        return toml::table{{"a", this->a}, {"b", this->b}};
+    }
+};
+} // extlib
+
+namespace toml
+{
+template<>
+struct from<extlib::foo>
+{
+    static extlib::foo from_toml(const toml::value& v)
+    {
+        return extlib::foo{toml::find<int>(v, "a"), toml::find<std::string>(v, "b")};
+    }
+};
+
+template<>
+struct into<extlib::foo>
+{
+    static toml::table into_toml(const extlib::foo& f)
+    {
+        return toml::table{{"a", f.a}, {"b", f.b}};
+    }
+};
+} // toml
+
+
+BOOST_AUTO_TEST_CASE(test_conversion_by_member_methods)
+{
+    const toml::value v{{"a", 42}, {"b", "baz"}};
+
+    const auto foo = toml::get<extlib::foo>(v);
+    BOOST_CHECK_EQUAL(foo.a, 42);
+    BOOST_CHECK_EQUAL(foo.b, "baz");
+
+    const toml::value v2(foo);
+
+    BOOST_CHECK_EQUAL(v, v2);
+}
+
+BOOST_AUTO_TEST_CASE(test_conversion_by_specialization)
+{
+    const toml::value v{{"a", 42}, {"b", "baz"}};
+
+    const auto bar = toml::get<extlib::bar>(v);
+    BOOST_CHECK_EQUAL(bar.a, 42);
+    BOOST_CHECK_EQUAL(bar.b, "baz");
+
+    const toml::value v2(bar);
+
+    BOOST_CHECK_EQUAL(v, v2);
+}
+
+BOOST_AUTO_TEST_CASE(test_recursive_conversion)
+{
+    const toml::value v{
+        toml::table{{"a", 42}, {"b", "baz"}},
+        toml::table{{"a", 43}, {"b", "qux"}},
+        toml::table{{"a", 44}, {"b", "quux"}},
+        toml::table{{"a", 45}, {"b", "foobar"}},
+    };
+
+    const auto foos = toml::get<std::vector<extlib::foo>>(v);
+    BOOST_CHECK_EQUAL(foos.size()  , 4ul);
+    BOOST_CHECK_EQUAL(foos.at(0).a , 42);
+    BOOST_CHECK_EQUAL(foos.at(1).a , 43);
+    BOOST_CHECK_EQUAL(foos.at(2).a , 44);
+    BOOST_CHECK_EQUAL(foos.at(3).a , 45);
+
+    BOOST_CHECK_EQUAL(foos.at(0).b , "baz");
+    BOOST_CHECK_EQUAL(foos.at(1).b , "qux");
+    BOOST_CHECK_EQUAL(foos.at(2).b , "quux");
+    BOOST_CHECK_EQUAL(foos.at(3).b , "foobar");
+
+    const auto bars = toml::get<std::vector<extlib::bar>>(v);
+    BOOST_CHECK_EQUAL(bars.size()  , 4ul);
+    BOOST_CHECK_EQUAL(bars.at(0).a , 42);
+    BOOST_CHECK_EQUAL(bars.at(1).a , 43);
+    BOOST_CHECK_EQUAL(bars.at(2).a , 44);
+    BOOST_CHECK_EQUAL(bars.at(3).a , 45);
+
+    BOOST_CHECK_EQUAL(bars.at(0).b , "baz");
+    BOOST_CHECK_EQUAL(bars.at(1).b , "qux");
+    BOOST_CHECK_EQUAL(bars.at(2).b , "quux");
+    BOOST_CHECK_EQUAL(bars.at(3).b , "foobar");
+}

tests/test_format_error.cpp

@@ -22,7 +22,7 @@ BOOST_AUTO_TEST_CASE(test_1_value)
     {
         const std::string pretty_error =
             toml::format_error("[error] test error", val, "this is a value",
-                               std::vector<std::string>{"this is a hint"});
+                               {"this is a hint"});
         std::cout << pretty_error << std::endl;
     }
 }
@@ -44,7 +44,7 @@ BOOST_AUTO_TEST_CASE(test_2_values)
             toml::format_error("[error] test error with two values",
                                v1, "this is the answer",
                                v2, "this is the pi",
-                               std::vector<std::string>{"hint"});
+                               {"hint"});
         std::cout << pretty_error << std::endl;
     }
 }
@@ -69,7 +69,7 @@ BOOST_AUTO_TEST_CASE(test_3_values)
                                v1, "this is the answer",
                                v2, "this is the pi",
                                v3, "this is a meta-syntactic variable",
-                               std::vector<std::string>{"hint 1", "hint 2"});
+                               {"hint 1", "hint 2"});
         std::cout << pretty_error << std::endl;
     }
 }

tests/test_get.cpp

@@ -12,6 +12,9 @@
 #include <list>
 #include <deque>
 #include <array>
+#if __cplusplus >= 201703L
+#include <string_view>
+#endif
 
 
 BOOST_AUTO_TEST_CASE(test_get_exact)
@@ -166,6 +169,17 @@ BOOST_AUTO_TEST_CASE(test_get_string_type)
         toml::get<std::string>(v) += "bar";
         BOOST_CHECK_EQUAL("foobar", toml::get<std::string>(v));
     }
+
+#if __cplusplus >= 201703L
+    {
+        toml::value v("foo", toml::string_t::basic);
+        BOOST_CHECK_EQUAL("foo", toml::get<std::string_view>(v));
+    }
+    {
+        toml::value v("foo", toml::string_t::literal);
+        BOOST_CHECK_EQUAL("foo", toml::get<std::string_view>(v));
+    }
+#endif
 }
 
 BOOST_AUTO_TEST_CASE(test_get_toml_array)

tests/test_get_related_func.cpp

@@ -45,21 +45,194 @@ BOOST_AUTO_TEST_CASE(test_find)
 
 BOOST_AUTO_TEST_CASE(test_get_or)
 {
-    {
+    // requires conversion int -> uint
-        toml::table v{{"num", 42}};
-        BOOST_CHECK_EQUAL(42, toml::get_or<int>(v, "num", 0));
-        BOOST_CHECK_EQUAL(0,  toml::get_or<int>(v, "foo", 0));
-    }
-    {
-        toml::value v = toml::table{{"num", 42}};
-        BOOST_CHECK_EQUAL(42, toml::get_or<int>(v, "num", 0));
-        BOOST_CHECK_EQUAL(0,  toml::get_or<int>(v, "foo", 0));
-    }
     {
         toml::value v1(42);
         toml::value v2(3.14);
-        BOOST_CHECK_EQUAL(42, toml::get_or<int>(v1, 0));
+        BOOST_CHECK_EQUAL(42u, toml::get_or(v1, 0u));
-        BOOST_CHECK_EQUAL(0,  toml::get_or<int>(v2, 0));
+        BOOST_CHECK_EQUAL(0u,  toml::get_or(v2, 0u));
+    }
+
+    // exact toml type
+    {
+        toml::value v1(42);
+        toml::value v2(3.14);
+
+        toml::integer opt(0);
+        BOOST_CHECK_EQUAL(42, toml::get_or(v1, opt));
+        BOOST_CHECK_EQUAL(0,  toml::get_or(v2, opt));
+
+        toml::value v3("foobar");
+        toml::string s("bazqux");
+
+        BOOST_CHECK_EQUAL("foobar", toml::get_or(v3, s));
+        BOOST_CHECK_EQUAL("bazqux", toml::get_or(v1, s));
+
+    }
+
+    // std::string
+    {
+        toml::value v1("foobar");
+        toml::value v2(42);
+
+        std::string       s1("bazqux");
+        const std::string s2("bazqux");
+
+        BOOST_CHECK_EQUAL("foobar", toml::get_or(v1, s1));
+        BOOST_CHECK_EQUAL("bazqux", toml::get_or(v2, s1));
+
+        std::string& v1r = toml::get_or(v1, s1);
+        std::string& s1r = toml::get_or(v2, s1);
+
+        BOOST_CHECK_EQUAL("foobar", v1r);
+        BOOST_CHECK_EQUAL("bazqux", s1r);
+
+        BOOST_CHECK_EQUAL("foobar", toml::get_or(v1, s2));
+        BOOST_CHECK_EQUAL("bazqux", toml::get_or(v2, s2));
+
+        BOOST_CHECK_EQUAL("foobar", toml::get_or(v1, std::move(s1)));
+        BOOST_CHECK_EQUAL("bazqux", toml::get_or(v2, std::move(s1)));
+    }
+
+    // string literal
+    {
+        toml::value v1("foobar");
+        toml::value v2(42);
+
+        BOOST_CHECK_EQUAL("foobar", toml::get_or(v1, "bazqux"));
+        BOOST_CHECK_EQUAL("bazqux", toml::get_or(v2, "bazqux"));
+
+        const char* lit = "bazqux";
+        BOOST_CHECK_EQUAL("foobar", toml::get_or(v1, lit));
+        BOOST_CHECK_EQUAL("bazqux", toml::get_or(v2, lit));
+    }
+}
+
+BOOST_AUTO_TEST_CASE(test_find_or)
+{
+    // ========================================================================
+    // pass toml::value
+    //
+    // requires conversion int -> uint
+    {
+        toml::table v{{"num", 42}};
+        BOOST_CHECK_EQUAL(42u, toml::find_or(v, "num", 0u));
+        BOOST_CHECK_EQUAL(0u,  toml::find_or(v, "foo", 0u));
+    }
+    // exact toml type
+    {
+        toml::table v1{{"key", 42  }};
+        toml::table v2{{"key", 3.14}};
+        toml::table v3{{"not", "key"}};
+
+        toml::integer opt(0);
+        BOOST_CHECK_EQUAL(42, toml::find_or(v1, "key", opt));
+        BOOST_CHECK_EQUAL(0,  toml::find_or(v2, "key", opt));
+        BOOST_CHECK_EQUAL(0,  toml::find_or(v3, "key", opt));
+
+        toml::table v4{{"str", "foobar"}};
+        toml::string s("bazqux");
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v4, "str", s));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v1, "str", s));
+    }
+    // std::string
+    {
+        toml::table v1{{"key", "foobar"}};
+        toml::table v2{{"key", 42}};
+
+        std::string       s1("bazqux");
+        const std::string s2("bazqux");
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v1, "key", s1));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v2, "key", s1));
+
+        std::string& v1r = toml::find_or(v1, "key", s1);
+        std::string& s1r = toml::find_or(v2, "key", s1);
+
+        BOOST_CHECK_EQUAL("foobar", v1r);
+        BOOST_CHECK_EQUAL("bazqux", s1r);
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v1, "key", s2));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v2, "key", s2));
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(std::move(v1), "key", std::move(s1)));
+        s1 = "bazqux"; // restoring moved value
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(std::move(v2), "key", std::move(s1)));
+    }
+    // string literal
+    {
+        toml::table v1{{"key", "foobar"}};
+        toml::table v2{{"key",42}};
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v1, "key", "bazqux"));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v2, "key", "bazqux"));
+
+        const char* lit = "bazqux";
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v1, "key", lit));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v2, "key", lit));
+    }
+
+    // ========================================================================
+    // pass toml::value
+    //
+    // requires conversion int -> uint
+    {
+        toml::table v = toml::table{{"num", 42}};
+        BOOST_CHECK_EQUAL(42u, toml::find_or(v, "num", 0u));
+        BOOST_CHECK_EQUAL(0u,  toml::find_or(v, "foo", 0u));
+    }
+    // exact toml type
+    {
+        toml::value v1 = toml::table{{"key", 42  }};
+        toml::value v2 = toml::table{{"key", 3.14}};
+        toml::value v3 = toml::table{{"not", "key"}};
+
+        BOOST_CHECK_EQUAL(42, toml::find_or(v1, "key", toml::integer(0)));
+        BOOST_CHECK_EQUAL( 0, toml::find_or(v2, "key", toml::integer(0)));
+        BOOST_CHECK_EQUAL( 0, toml::find_or(v3, "key", toml::integer(0)));
+
+        toml::value v4 = toml::table{{"str", "foobar"}};
+        toml::string s("bazqux");
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v4, "str", s));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v1, "str", s));
+    }
+    // std::string
+    {
+        toml::value v1 = toml::table{{"key", "foobar"}};
+        toml::value v2 = toml::table{{"key", 42}};
+
+        std::string       s1("bazqux");
+        const std::string s2("bazqux");
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v1, "key", s1));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v2, "key", s1));
+
+        std::string& v1r = toml::find_or(v1, "key", s1);
+        std::string& s1r = toml::find_or(v2, "key", s1);
+
+        BOOST_CHECK_EQUAL("foobar", v1r);
+        BOOST_CHECK_EQUAL("bazqux", s1r);
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v1, "key", s2));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v2, "key", s2));
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(std::move(v1), "key", std::move(s1)));
+        s1 = "bazqux"; // restoring moved value
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(std::move(v2), "key", std::move(s1)));
+    }
+    // string literal
+    {
+        toml::value v1 = toml::table{{"key", "foobar"}};
+        toml::value v2 = toml::table{{"key",42}};
+
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v1, "key", "bazqux"));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v2, "key", "bazqux"));
+
+        const char* lit = "bazqux";
+        BOOST_CHECK_EQUAL("foobar", toml::find_or(v1, "key", lit));
+        BOOST_CHECK_EQUAL("bazqux", toml::find_or(v2, "key", lit));
     }
 }
 

tests/test_literals.cpp

@@ -0,0 +1,154 @@
+#define BOOST_TEST_MODULE "test_literals"
+#ifdef UNITTEST_FRAMEWORK_LIBRARY_EXIST
+#include <boost/test/unit_test.hpp>
+#else
+#define BOOST_TEST_NO_LIB
+#include <boost/test/included/unit_test.hpp>
+#endif
+#include <toml.hpp>
+#include <map>
+
+BOOST_AUTO_TEST_CASE(test_file_as_literal)
+{
+    using namespace toml::literals::toml_literals;
+
+    {
+        const toml::value r{{"a", 42}, {"b", "baz"}};
+        const toml::value v = u8R"(
+            a = 42
+            b = "baz"
+        )"_toml;
+
+        BOOST_CHECK_EQUAL(r, v);
+    }
+    {
+        const toml::value r{
+            {"c", 3.14},
+            {"table", toml::table{{"a", 42}, {"b", "baz"}}}
+        };
+        const toml::value v = u8R"(
+            c = 3.14
+            [table]
+            a = 42
+            b = "baz"
+        )"_toml;
+
+        BOOST_CHECK_EQUAL(r, v);
+    }
+    {
+        const toml::value r{
+            {"table", toml::table{{"a", 42}, {"b", "baz"}}}
+        };
+        const toml::value v = u8R"(
+            [table]
+            a = 42
+            b = "baz"
+        )"_toml;
+
+        BOOST_CHECK_EQUAL(r, v);
+    }
+}
+
+BOOST_AUTO_TEST_CASE(test_value_as_literal)
+{
+    using namespace toml::literals::toml_literals;
+
+    {
+        const toml::value v1 = u8"true"_toml;
+        const toml::value v2 = u8"false"_toml;
+
+        BOOST_CHECK(v1.is_boolean());
+        BOOST_CHECK(v2.is_boolean());
+        BOOST_CHECK(toml::get<bool>(v1));
+        BOOST_CHECK(!toml::get<bool>(v2));
+    }
+    {
+        const toml::value v1 = u8"123_456"_toml;
+        const toml::value v2 = u8"0b0010"_toml;
+        const toml::value v3 = u8"0xDEADBEEF"_toml;
+
+        BOOST_CHECK(v1.is_integer());
+        BOOST_CHECK(v2.is_integer());
+        BOOST_CHECK(v3.is_integer());
+        BOOST_CHECK_EQUAL(toml::get<toml::integer>(v1), 123456);
+        BOOST_CHECK_EQUAL(toml::get<toml::integer>(v2), 2);
+        BOOST_CHECK_EQUAL(toml::get<toml::integer>(v3), 0xDEADBEEF);
+    }
+    {
+        const toml::value v1 = u8"3.1415"_toml;
+        const toml::value v2 = u8"6.02e+23"_toml;
+
+        BOOST_CHECK(v1.is_float());
+        BOOST_CHECK(v2.is_float());
+        BOOST_CHECK_CLOSE(toml::get<double>(v1), 3.1415,  0.00001);
+        BOOST_CHECK_CLOSE(toml::get<double>(v2), 6.02e23, 0.0001);
+    }
+    {
+        const toml::value v1 = u8R"("foo")"_toml;
+        const toml::value v2 = u8R"('foo')"_toml;
+        const toml::value v3 = u8R"("""foo""")"_toml;
+        const toml::value v4 = u8R"('''foo''')"_toml;
+
+        BOOST_CHECK(v1.is_string());
+        BOOST_CHECK(v2.is_string());
+        BOOST_CHECK(v3.is_string());
+        BOOST_CHECK(v4.is_string());
+        BOOST_CHECK_EQUAL(toml::get<std::string>(v1), "foo");
+        BOOST_CHECK_EQUAL(toml::get<std::string>(v2), "foo");
+        BOOST_CHECK_EQUAL(toml::get<std::string>(v3), "foo");
+        BOOST_CHECK_EQUAL(toml::get<std::string>(v4), "foo");
+    }
+    {
+        const toml::value v1 = u8R"([1,2,3])"_toml;
+
+        BOOST_CHECK(v1.is_array());
+        BOOST_CHECK((toml::get<std::vector<int>>(v1) == std::vector<int>{1,2,3}));
+
+        const toml::value v2 = u8R"([1,])"_toml;
+
+        BOOST_CHECK(v2.is_array());
+        BOOST_CHECK((toml::get<std::vector<int>>(v2) == std::vector<int>{1}));
+
+        const toml::value v3 = u8R"([[1,]])"_toml;
+        BOOST_CHECK(v3.is_array());
+        BOOST_CHECK((toml::get<std::vector<int>>(toml::get<toml::array>(v3).front()) == std::vector<int>{1}));
+
+        const toml::value v4 = u8R"([[1],])"_toml;
+        BOOST_CHECK(v4.is_array());
+        BOOST_CHECK((toml::get<std::vector<int>>(toml::get<toml::array>(v4).front()) == std::vector<int>{1}));
+    }
+    {
+        const toml::value v1 = u8R"({a = 42})"_toml;
+
+        BOOST_CHECK(v1.is_table());
+        BOOST_CHECK((toml::get<std::map<std::string,int>>(v1) ==
+                               std::map<std::string,int>{{"a", 42}}));
+    }
+    {
+        const toml::value v1 = u8"1979-05-27"_toml;
+
+        BOOST_CHECK(v1.is_local_date());
+        BOOST_CHECK_EQUAL(toml::get<toml::local_date>(v1),
+                          toml::local_date(1979, toml::month_t::May, 27));
+    }
+    {
+        const toml::value v1 = u8"12:00:00"_toml;
+
+        BOOST_CHECK(v1.is_local_time());
+        BOOST_CHECK(toml::get<std::chrono::hours>(v1) == std::chrono::hours(12));
+    }
+    {
+        const toml::value v1 = u8"1979-05-27T07:32:00"_toml;
+        BOOST_CHECK(v1.is_local_datetime());
+        BOOST_CHECK_EQUAL(toml::get<toml::local_datetime>(v1),
+            toml::local_datetime(toml::local_date(1979, toml::month_t::May, 27),
+                                 toml::local_time(7, 32, 0)));
+    }
+    {
+        const toml::value v1 = "1979-05-27T07:32:00Z"_toml;
+        BOOST_CHECK(v1.is_offset_datetime());
+        BOOST_CHECK_EQUAL(toml::get<toml::offset_datetime>(v1),
+            toml::offset_datetime(toml::local_date(1979, toml::month_t::May, 27),
+                                  toml::local_time(7, 32, 0), toml::time_offset(0, 0)));
+    }
+}

tests/test_multiple_translation_unit_1.cpp

@@ -0,0 +1,11 @@
+#include <toml.hpp>
+
+int read_a(const toml::table&);
+
+int main()
+{
+    const std::string content("a = 0");
+    std::istringstream iss(content);
+    const auto data = toml::parse(iss, "test_multiple_translation_unit.toml");
+    return read_a(data);
+}

tests/test_multiple_translation_unit_2.cpp

@@ -0,0 +1,6 @@
+#include <toml.hpp>
+
+int read_a(const toml::table& t)
+{
+    return toml::get<int>(t.at("a"));
+}

tests/test_to_toml.cpp

@@ -1,189 +0,0 @@
-#define BOOST_TEST_MODULE "test_to_toml"
-#ifdef UNITTEST_FRAMEWORK_LIBRARY_EXIST
-#include <boost/test/unit_test.hpp>
-#else
-#define BOOST_TEST_NO_LIB
-#include <boost/test/included/unit_test.hpp>
-#endif
-#include <toml.hpp>
-#include <map>
-#include <list>
-
-BOOST_AUTO_TEST_CASE(test_value_boolean)
-{
-    toml::value v1 = toml::to_toml(true);
-    toml::value v2 = toml::to_toml(false);
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Boolean);
-    BOOST_CHECK_EQUAL(v2.type(), toml::value_t::Boolean);
-    BOOST_CHECK(v1.is(toml::value_t::Boolean));
-    BOOST_CHECK(v2.is(toml::value_t::Boolean));
-    BOOST_CHECK(v1.is<toml::Boolean>());
-    BOOST_CHECK(v2.is<toml::Boolean>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Boolean>(), false);
-}
-
-BOOST_AUTO_TEST_CASE(test_value_integer)
-{
-    toml::value v1 = toml::to_toml(-42);
-    toml::value v2 = toml::to_toml(42u);
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Integer);
-    BOOST_CHECK_EQUAL(v2.type(), toml::value_t::Integer);
-    BOOST_CHECK(v1.is(toml::value_t::Integer));
-    BOOST_CHECK(v2.is(toml::value_t::Integer));
-    BOOST_CHECK(v1.is<toml::Integer>());
-    BOOST_CHECK(v2.is<toml::Integer>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Integer>(), -42);
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Integer>(),  42u);
-}
-
-BOOST_AUTO_TEST_CASE(test_value_float)
-{
-    toml::value v1 = toml::to_toml(3.14);
-    toml::value v2 = toml::to_toml(3.14f);
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Float);
-    BOOST_CHECK_EQUAL(v2.type(), toml::value_t::Float);
-    BOOST_CHECK(v1.is(toml::value_t::Float));
-    BOOST_CHECK(v2.is(toml::value_t::Float));
-    BOOST_CHECK(v1.is<toml::Float>());
-    BOOST_CHECK(v2.is<toml::Float>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Float>(), 3.14);
-    BOOST_CHECK_CLOSE_FRACTION(v2.cast<toml::value_t::Float>(), 3.14, 1e-2);
-}
-
-BOOST_AUTO_TEST_CASE(test_value_string)
-{
-    toml::value v1 = toml::to_toml(std::string("foo"));
-    toml::value v2 = toml::to_toml(std::string("foo"), toml::string_t::literal);
-    toml::value v3 = toml::to_toml("foo");
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::String);
-    BOOST_CHECK_EQUAL(v2.type(), toml::value_t::String);
-    BOOST_CHECK_EQUAL(v3.type(), toml::value_t::String);
-    BOOST_CHECK(v1.is(toml::value_t::String));
-    BOOST_CHECK(v2.is(toml::value_t::String));
-    BOOST_CHECK(v3.is(toml::value_t::String));
-    BOOST_CHECK(v1.is<toml::String>());
-    BOOST_CHECK(v2.is<toml::String>());
-    BOOST_CHECK(v3.is<toml::String>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::String>(), "foo");
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::String>(), "foo");
-    BOOST_CHECK_EQUAL(v3.cast<toml::value_t::String>(), "foo");
-}
-
-BOOST_AUTO_TEST_CASE(test_value_local_date)
-{
-    toml::value v1 = toml::to_toml(toml::local_date(2018, toml::month_t::Jan, 31));
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::LocalDate);
-    BOOST_CHECK(v1.is(toml::value_t::LocalDate));
-    BOOST_CHECK(v1.is<toml::LocalDate>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalDate>(),
-                      toml::local_date(2018, toml::month_t::Jan, 31));
-}
-
-BOOST_AUTO_TEST_CASE(test_value_local_time)
-{
-    toml::value v1 = toml::to_toml(toml::local_time(12, 30, 45));
-    toml::value v2 = toml::to_toml(std::chrono::hours(12) + std::chrono::minutes(30) +
-                   std::chrono::seconds(45));
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::LocalTime);
-    BOOST_CHECK_EQUAL(v2.type(), toml::value_t::LocalTime);
-    BOOST_CHECK(v1.is(toml::value_t::LocalTime));
-    BOOST_CHECK(v2.is(toml::value_t::LocalTime));
-    BOOST_CHECK(v1.is<toml::LocalTime>());
-    BOOST_CHECK(v2.is<toml::LocalTime>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalTime>(),
-                      toml::local_time(12, 30, 45));
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::LocalTime>(),
-                      toml::local_time(12, 30, 45));
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalTime>(),
-                      v2.cast<toml::value_t::LocalTime>());
-}
-
-BOOST_AUTO_TEST_CASE(test_value_local_datetime)
-{
-    toml::value v1 = toml::to_toml(toml::local_datetime(
-                toml::local_date(2018, toml::month_t::Jan, 31),
-                toml::local_time(12, 30, 45)
-                ));
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::LocalDatetime);
-    BOOST_CHECK(v1.is(toml::value_t::LocalDatetime));
-    BOOST_CHECK(v1.is<toml::LocalDatetime>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalDatetime>(),
-                      toml::local_datetime(
-                          toml::local_date(2018, toml::month_t::Jan, 31),
-                          toml::local_time(12, 30, 45)));
-}
-
-BOOST_AUTO_TEST_CASE(test_value_offset_datetime)
-{
-    toml::value v1 = toml::to_toml(toml::offset_datetime(
-                toml::local_date(2018, toml::month_t::Jan, 31),
-                toml::local_time(12, 30, 45),
-                toml::time_offset(9, 0)
-                ));
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::OffsetDatetime);
-    BOOST_CHECK(v1.is(toml::value_t::OffsetDatetime));
-    BOOST_CHECK(v1.is<toml::OffsetDatetime>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::OffsetDatetime>(),
-            toml::offset_datetime(
-                toml::local_date(2018, toml::month_t::Jan, 31),
-                toml::local_time(12, 30, 45),
-                toml::time_offset(9, 0)
-                ));
-}
-
-BOOST_AUTO_TEST_CASE(test_value_array)
-{
-    std::vector<int> v{1,2,3,4,5};
-    toml::value v1 = toml::to_toml(v);
-    toml::value v2 = toml::to_toml(6,7,8,9,0);
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Array);
-    BOOST_CHECK(v1.is(toml::value_t::Array));
-    BOOST_CHECK(v1.is<toml::Array>());
-
-    BOOST_CHECK_EQUAL(v2.type(), toml::value_t::Array);
-    BOOST_CHECK(v2.is(toml::value_t::Array));
-    BOOST_CHECK(v2.is<toml::Array>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(0).cast<toml::value_t::Integer>(), 1);
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(1).cast<toml::value_t::Integer>(), 2);
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(2).cast<toml::value_t::Integer>(), 3);
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(3).cast<toml::value_t::Integer>(), 4);
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(4).cast<toml::value_t::Integer>(), 5);
-
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(0).cast<toml::value_t::Integer>(), 6);
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(1).cast<toml::value_t::Integer>(), 7);
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(2).cast<toml::value_t::Integer>(), 8);
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(3).cast<toml::value_t::Integer>(), 9);
-    BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(4).cast<toml::value_t::Integer>(), 0);
-}
-
-BOOST_AUTO_TEST_CASE(test_value_table)
-{
-    toml::value v1 = toml::to_toml({{"foo", 42}, {"bar", 3.14}, {"baz", "qux"}});
-
-    BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Table);
-    BOOST_CHECK(v1.is(toml::value_t::Table));
-    BOOST_CHECK(v1.is<toml::Table>());
-
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("foo").cast<toml::value_t::Integer>(),    42);
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("bar").cast<toml::value_t::Float>(),      3.14);
-    BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("baz").cast<toml::value_t::String>().str, "qux");
-}

tests/test_value.cpp

@@ -9,6 +9,11 @@
 #include <map>
 #include <list>
 
+#if __cplusplus >= 201703L
+#include <string_view>
+#endif
+
+
 BOOST_AUTO_TEST_CASE(test_value_boolean)
 {
     toml::value v1(true);
@@ -20,9 +25,13 @@ BOOST_AUTO_TEST_CASE(test_value_boolean)
     BOOST_CHECK(v2.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
     BOOST_CHECK(v2.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
+    BOOST_CHECK(v2.is_boolean());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Boolean>(), false);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
+    BOOST_CHECK_EQUAL(v2.as_boolean(), false);
 
     v1 = false;
     v2 = true;
@@ -33,9 +42,13 @@ BOOST_AUTO_TEST_CASE(test_value_boolean)
     BOOST_CHECK(v2.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
     BOOST_CHECK(v2.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
+    BOOST_CHECK(v2.is_boolean());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), false);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), false);
+    BOOST_CHECK_EQUAL(v2.as_boolean(), true);
 
     toml::value v3(v1);
     toml::value v4(v2);
@@ -48,9 +61,13 @@ BOOST_AUTO_TEST_CASE(test_value_boolean)
     BOOST_CHECK(v4.is(toml::value_t::Boolean));
     BOOST_CHECK(v3.is<toml::Boolean>());
     BOOST_CHECK(v4.is<toml::Boolean>());
+    BOOST_CHECK(v3.is_boolean());
+    BOOST_CHECK(v4.is_boolean());
 
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Boolean>(), false);
     BOOST_CHECK_EQUAL(v4.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v3.as_boolean(), false);
+    BOOST_CHECK_EQUAL(v4.as_boolean(), true);
 
     toml::value v5(std::move(v1));
     toml::value v6(std::move(v2));
@@ -61,9 +78,13 @@ BOOST_AUTO_TEST_CASE(test_value_boolean)
     BOOST_CHECK(v6.is(toml::value_t::Boolean));
     BOOST_CHECK(v5.is<toml::Boolean>());
     BOOST_CHECK(v6.is<toml::Boolean>());
+    BOOST_CHECK(v3.is_boolean());
+    BOOST_CHECK(v4.is_boolean());
 
     BOOST_CHECK_EQUAL(v5.cast<toml::value_t::Boolean>(), false);
     BOOST_CHECK_EQUAL(v6.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v5.as_boolean(), false);
+    BOOST_CHECK_EQUAL(v6.as_boolean(), true);
 
     v1 = 42;
     v2 = 3.14;
@@ -74,9 +95,13 @@ BOOST_AUTO_TEST_CASE(test_value_boolean)
     BOOST_CHECK(v2.is(toml::value_t::Float));
     BOOST_CHECK(v1.is<toml::Integer>());
     BOOST_CHECK(v2.is<toml::Float>());
+    BOOST_CHECK(v1.is_integer());
+    BOOST_CHECK(v2.is_float());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Integer>(), 42);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Float>(),   3.14);
+    BOOST_CHECK_EQUAL(v1.as_integer(),  42);
+    BOOST_CHECK_EQUAL(v2.as_float(), 3.14);
 }
 
 BOOST_AUTO_TEST_CASE(test_value_integer)
@@ -90,9 +115,13 @@ BOOST_AUTO_TEST_CASE(test_value_integer)
     BOOST_CHECK(v2.is(toml::value_t::Integer));
     BOOST_CHECK(v1.is<toml::Integer>());
     BOOST_CHECK(v2.is<toml::Integer>());
+    BOOST_CHECK(v1.is_integer());
+    BOOST_CHECK(v2.is_integer());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Integer>(), -42);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Integer>(),  42u);
+    BOOST_CHECK_EQUAL(v1.as_integer(), -42);
+    BOOST_CHECK_EQUAL(v2.as_integer(),  42u);
 
     v1 = 54;
     v2 = -54;
@@ -103,9 +132,13 @@ BOOST_AUTO_TEST_CASE(test_value_integer)
     BOOST_CHECK(v2.is(toml::value_t::Integer));
     BOOST_CHECK(v1.is<toml::Integer>());
     BOOST_CHECK(v2.is<toml::Integer>());
+    BOOST_CHECK(v1.is_integer());
+    BOOST_CHECK(v2.is_integer());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Integer>(),  54);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Integer>(), -54);
+    BOOST_CHECK_EQUAL(v1.as_integer(),  54);
+    BOOST_CHECK_EQUAL(v2.as_integer(), -54);
 
     toml::value v3(v1);
     toml::value v4(v2);
@@ -118,9 +151,13 @@ BOOST_AUTO_TEST_CASE(test_value_integer)
     BOOST_CHECK(v4.is(toml::value_t::Integer));
     BOOST_CHECK(v3.is<toml::Integer>());
     BOOST_CHECK(v4.is<toml::Integer>());
+    BOOST_CHECK(v3.is_integer());
+    BOOST_CHECK(v4.is_integer());
 
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Integer>(),  54);
     BOOST_CHECK_EQUAL(v4.cast<toml::value_t::Integer>(), -54);
+    BOOST_CHECK_EQUAL(v3.as_integer(),  54);
+    BOOST_CHECK_EQUAL(v4.as_integer(), -54);
 
     toml::value v5(std::move(v1));
     toml::value v6(std::move(v2));
@@ -131,9 +168,13 @@ BOOST_AUTO_TEST_CASE(test_value_integer)
     BOOST_CHECK(v6.is(toml::value_t::Integer));
     BOOST_CHECK(v5.is<toml::Integer>());
     BOOST_CHECK(v6.is<toml::Integer>());
+    BOOST_CHECK(v5.is_integer());
+    BOOST_CHECK(v6.is_integer());
 
     BOOST_CHECK_EQUAL(v5.cast<toml::value_t::Integer>(),  54);
     BOOST_CHECK_EQUAL(v6.cast<toml::value_t::Integer>(), -54);
+    BOOST_CHECK_EQUAL(v5.as_integer(),  54);
+    BOOST_CHECK_EQUAL(v6.as_integer(), -54);
 
     v1 = true;
     v2 = false;
@@ -144,9 +185,13 @@ BOOST_AUTO_TEST_CASE(test_value_integer)
     BOOST_CHECK(v2.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
     BOOST_CHECK(v2.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
+    BOOST_CHECK(v2.is_boolean());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Boolean>(), false);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
+    BOOST_CHECK_EQUAL(v2.as_boolean(), false);
 }
 
 BOOST_AUTO_TEST_CASE(test_value_float)
@@ -160,9 +205,13 @@ BOOST_AUTO_TEST_CASE(test_value_float)
     BOOST_CHECK(v2.is(toml::value_t::Float));
     BOOST_CHECK(v1.is<toml::Float>());
     BOOST_CHECK(v2.is<toml::Float>());
+    BOOST_CHECK(v1.is_float());
+    BOOST_CHECK(v2.is_float());
 
     BOOST_CHECK_EQUAL         (v1.cast<toml::value_t::Float>(), 3.14);
     BOOST_CHECK_CLOSE_FRACTION(v2.cast<toml::value_t::Float>(), 3.14, 1e-2);
+    BOOST_CHECK_EQUAL         (v1.as_float(), 3.14);
+    BOOST_CHECK_CLOSE_FRACTION(v2.as_float(), 3.14, 1e-2);
 
     v1 = 2.718f;
     v2 = 2.718;
@@ -173,9 +222,13 @@ BOOST_AUTO_TEST_CASE(test_value_float)
     BOOST_CHECK(v2.is(toml::value_t::Float));
     BOOST_CHECK(v1.is<toml::Float>());
     BOOST_CHECK(v2.is<toml::Float>());
+    BOOST_CHECK(v1.is_float());
+    BOOST_CHECK(v2.is_float());
 
     BOOST_CHECK_CLOSE_FRACTION(v1.cast<toml::value_t::Float>(), 2.718, 1e-3);
     BOOST_CHECK_EQUAL         (v2.cast<toml::value_t::Float>(), 2.718);
+    BOOST_CHECK_CLOSE_FRACTION(v1.as_float(), 2.718, 1e-3);
+    BOOST_CHECK_EQUAL         (v2.as_float(), 2.718);
 
     toml::value v3(v1);
     toml::value v4(v2);
@@ -188,9 +241,13 @@ BOOST_AUTO_TEST_CASE(test_value_float)
     BOOST_CHECK(v4.is(toml::value_t::Float));
     BOOST_CHECK(v3.is<toml::Float>());
     BOOST_CHECK(v4.is<toml::Float>());
+    BOOST_CHECK(v3.is_float());
+    BOOST_CHECK(v4.is_float());
 
     BOOST_CHECK_CLOSE_FRACTION(v3.cast<toml::value_t::Float>(), 2.718, 1e-3);
     BOOST_CHECK_EQUAL         (v4.cast<toml::value_t::Float>(), 2.718);
+    BOOST_CHECK_CLOSE_FRACTION(v3.as_float(), 2.718, 1e-3);
+    BOOST_CHECK_EQUAL         (v4.as_float(), 2.718);
 
     toml::value v5(std::move(v1));
     toml::value v6(std::move(v2));
@@ -201,9 +258,13 @@ BOOST_AUTO_TEST_CASE(test_value_float)
     BOOST_CHECK(v6.is(toml::value_t::Float));
     BOOST_CHECK(v5.is<toml::Float>());
     BOOST_CHECK(v6.is<toml::Float>());
+    BOOST_CHECK(v5.is_float());
+    BOOST_CHECK(v6.is_float());
 
     BOOST_CHECK_CLOSE_FRACTION(v5.cast<toml::value_t::Float>(), 2.718, 1e-3);
     BOOST_CHECK_EQUAL         (v6.cast<toml::value_t::Float>(), 2.718);
+    BOOST_CHECK_CLOSE_FRACTION(v5.as_float(), 2.718, 1e-3);
+    BOOST_CHECK_EQUAL         (v6.as_float(), 2.718);
 
     v1 = true;
     v2 = false;
@@ -214,9 +275,13 @@ BOOST_AUTO_TEST_CASE(test_value_float)
     BOOST_CHECK(v2.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
     BOOST_CHECK(v2.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
+    BOOST_CHECK(v2.is_boolean());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Boolean>(), false);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
+    BOOST_CHECK_EQUAL(v2.as_boolean(), false);
 }
 
 BOOST_AUTO_TEST_CASE(test_value_string)
@@ -234,10 +299,17 @@ BOOST_AUTO_TEST_CASE(test_value_string)
     BOOST_CHECK(v1.is<toml::String>());
     BOOST_CHECK(v2.is<toml::String>());
     BOOST_CHECK(v3.is<toml::String>());
+    BOOST_CHECK(v1.is_string());
+    BOOST_CHECK(v2.is_string());
+    BOOST_CHECK(v3.is_string());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::String>(), "foo");
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::String>(), "foo");
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::String>(), "foo");
+    BOOST_CHECK_EQUAL(v1.as_string(), "foo");
+    BOOST_CHECK_EQUAL(v2.as_string(), "foo");
+    BOOST_CHECK_EQUAL(v3.as_string(), "foo");
+
 
     v1 = "bar";
     v2 = "bar";
@@ -249,13 +321,17 @@ BOOST_AUTO_TEST_CASE(test_value_string)
     BOOST_CHECK(v1.is(toml::value_t::String));
     BOOST_CHECK(v2.is(toml::value_t::String));
     BOOST_CHECK(v3.is(toml::value_t::String));
-    BOOST_CHECK(v1.is<toml::String>());
+    BOOST_CHECK(v1.is_string());
-    BOOST_CHECK(v2.is<toml::String>());
+    BOOST_CHECK(v2.is_string());
-    BOOST_CHECK(v3.is<toml::String>());
+    BOOST_CHECK(v3.is_string());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::String>(), "bar");
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::String>(), "bar");
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::String>(), "bar");
+    BOOST_CHECK_EQUAL(v1.as_string(), "bar");
+    BOOST_CHECK_EQUAL(v2.as_string(), "bar");
+    BOOST_CHECK_EQUAL(v3.as_string(), "bar");
+
 
     toml::value v4(v1);
     toml::value v5(v2);
@@ -273,10 +349,17 @@ BOOST_AUTO_TEST_CASE(test_value_string)
     BOOST_CHECK(v4.is<toml::String>());
     BOOST_CHECK(v5.is<toml::String>());
     BOOST_CHECK(v6.is<toml::String>());
+    BOOST_CHECK(v4.is_string());
+    BOOST_CHECK(v5.is_string());
+    BOOST_CHECK(v6.is_string());
 
     BOOST_CHECK_EQUAL(v4.cast<toml::value_t::String>(), "bar");
     BOOST_CHECK_EQUAL(v5.cast<toml::value_t::String>(), "bar");
     BOOST_CHECK_EQUAL(v6.cast<toml::value_t::String>(), "bar");
+    BOOST_CHECK_EQUAL(v4.as_string(), "bar");
+    BOOST_CHECK_EQUAL(v5.as_string(), "bar");
+    BOOST_CHECK_EQUAL(v6.as_string(), "bar");
+
 
     v4.cast<toml::value_t::String>().str.at(2) = 'z';
     v5.cast<toml::value_t::String>().str.at(2) = 'z';
@@ -291,10 +374,13 @@ BOOST_AUTO_TEST_CASE(test_value_string)
     BOOST_CHECK(v4.is<toml::String>());
     BOOST_CHECK(v5.is<toml::String>());
     BOOST_CHECK(v6.is<toml::String>());
+    BOOST_CHECK(v4.is_string());
+    BOOST_CHECK(v5.is_string());
+    BOOST_CHECK(v6.is_string());
 
-    BOOST_CHECK_EQUAL(v4.cast<toml::value_t::String>(), "baz");
+    BOOST_CHECK_EQUAL(v4.as_string(), "baz");
-    BOOST_CHECK_EQUAL(v5.cast<toml::value_t::String>(), "baz");
+    BOOST_CHECK_EQUAL(v5.as_string(), "baz");
-    BOOST_CHECK_EQUAL(v6.cast<toml::value_t::String>(), "baz");
+    BOOST_CHECK_EQUAL(v6.as_string(), "baz");
 
     v1 = true;
     v2 = true;
@@ -309,10 +395,35 @@ BOOST_AUTO_TEST_CASE(test_value_string)
     BOOST_CHECK(v1.is<toml::Boolean>());
     BOOST_CHECK(v2.is<toml::Boolean>());
     BOOST_CHECK(v3.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
+    BOOST_CHECK(v2.is_boolean());
+    BOOST_CHECK(v3.is_boolean());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Boolean>(), true);
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
+    BOOST_CHECK_EQUAL(v2.as_boolean(), true);
+    BOOST_CHECK_EQUAL(v3.as_boolean(), true);
+
+#if __cplusplus >= 201703L
+    std::string_view sv = "foo";
+
+    toml::value v7(sv);
+    toml::value v8(sv, toml::string_t::literal);
+
+    BOOST_CHECK_EQUAL(v7.type(), toml::value_t::String);
+    BOOST_CHECK_EQUAL(v8.type(), toml::value_t::String);
+    BOOST_CHECK(v7.is(toml::value_t::String));
+    BOOST_CHECK(v8.is(toml::value_t::String));
+    BOOST_CHECK(v7.is<toml::String>());
+    BOOST_CHECK(v8.is<toml::String>());
+    BOOST_CHECK(v7.is_string());
+    BOOST_CHECK(v8.is_string());
+
+    BOOST_CHECK_EQUAL(v7.cast<toml::value_t::String>(), "foo");
+    BOOST_CHECK_EQUAL(v8.cast<toml::value_t::String>(), "foo");
+#endif
 }
 
 BOOST_AUTO_TEST_CASE(test_value_local_date)
@@ -322,18 +433,24 @@ BOOST_AUTO_TEST_CASE(test_value_local_date)
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::LocalDate);
     BOOST_CHECK(v1.is(toml::value_t::LocalDate));
     BOOST_CHECK(v1.is<toml::LocalDate>());
+    BOOST_CHECK(v1.is_local_date());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalDate>(),
                       toml::local_date(2018, toml::month_t::Jan, 31));
+    BOOST_CHECK_EQUAL(v1.as_local_date(),
+                      toml::local_date(2018, toml::month_t::Jan, 31));
 
     v1 = toml::local_date(2018, toml::month_t::Apr, 1);
 
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::LocalDate);
     BOOST_CHECK(v1.is(toml::value_t::LocalDate));
     BOOST_CHECK(v1.is<toml::LocalDate>());
+    BOOST_CHECK(v1.is_local_date());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalDate>(),
                       toml::local_date(2018, toml::month_t::Apr, 1));
+    BOOST_CHECK_EQUAL(v1.as_local_date(),
+                      toml::local_date(2018, toml::month_t::Apr, 1));
 
     toml::value v2(v1);
     BOOST_CHECK(v2 == v1);
@@ -341,15 +458,20 @@ BOOST_AUTO_TEST_CASE(test_value_local_date)
     BOOST_CHECK_EQUAL(v2.type(), toml::value_t::LocalDate);
     BOOST_CHECK(v2.is(toml::value_t::LocalDate));
     BOOST_CHECK(v2.is<toml::LocalDate>());
+    BOOST_CHECK(v2.is_local_date());
 
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::LocalDate>(),
                       toml::local_date(2018, toml::month_t::Apr, 1));
+    BOOST_CHECK_EQUAL(v2.as_local_date(),
+                      toml::local_date(2018, toml::month_t::Apr, 1));
 
     v1 = true;
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Boolean);
     BOOST_CHECK(v1.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
 }
 
 BOOST_AUTO_TEST_CASE(test_value_local_time)
@@ -364,21 +486,34 @@ BOOST_AUTO_TEST_CASE(test_value_local_time)
     BOOST_CHECK(v2.is(toml::value_t::LocalTime));
     BOOST_CHECK(v1.is<toml::LocalTime>());
     BOOST_CHECK(v2.is<toml::LocalTime>());
+    BOOST_CHECK(v1.is_local_time());
+    BOOST_CHECK(v2.is_local_time());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalTime>(),
                       toml::local_time(12, 30, 45));
+    BOOST_CHECK_EQUAL(v1.as_local_time(),
+                      toml::local_time(12, 30, 45));
+
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::LocalTime>(),
                       toml::local_time(12, 30, 45));
+    BOOST_CHECK_EQUAL(v2.as_local_time(),
+                      toml::local_time(12, 30, 45));
+
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalTime>(),
                       v2.cast<toml::value_t::LocalTime>());
+    BOOST_CHECK_EQUAL(v1.as_local_time(),
+                      v2.as_local_time());
 
     v1 = toml::local_time(1, 30, 0, /*ms*/ 100, /*us*/ 0);
 
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::LocalTime);
     BOOST_CHECK(v1.is(toml::value_t::LocalTime));
     BOOST_CHECK(v1.is<toml::LocalTime>());
+    BOOST_CHECK(v1.is_local_time());
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalTime>(),
                       toml::local_time(1, 30, 0, 100, 0));
+    BOOST_CHECK_EQUAL(v1.as_local_time(),
+                      toml::local_time(1, 30, 0, 100, 0));
 
     toml::value v3(v1);
     BOOST_CHECK(v3 == v1);
@@ -386,15 +521,20 @@ BOOST_AUTO_TEST_CASE(test_value_local_time)
     BOOST_CHECK_EQUAL(v3.type(), toml::value_t::LocalTime);
     BOOST_CHECK(v3.is(toml::value_t::LocalTime));
     BOOST_CHECK(v3.is<toml::LocalTime>());
+    BOOST_CHECK(v3.is_local_time());
 
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::LocalTime>(),
                       toml::local_time(1, 30, 0, 100, 0));
+    BOOST_CHECK_EQUAL(v3.as_local_time(),
+                      toml::local_time(1, 30, 0, 100, 0));
 
     v1 = true;
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Boolean);
     BOOST_CHECK(v1.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
 }
 
 BOOST_AUTO_TEST_CASE(test_value_local_datetime)
@@ -407,11 +547,16 @@ BOOST_AUTO_TEST_CASE(test_value_local_datetime)
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::LocalDatetime);
     BOOST_CHECK(v1.is(toml::value_t::LocalDatetime));
     BOOST_CHECK(v1.is<toml::LocalDatetime>());
+    BOOST_CHECK(v1.is_local_datetime());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalDatetime>(),
                       toml::local_datetime(
                           toml::local_date(2018, toml::month_t::Jan, 31),
                           toml::local_time(12, 30, 45)));
+    BOOST_CHECK_EQUAL(v1.as_local_datetime(),
+                      toml::local_datetime(
+                          toml::local_date(2018, toml::month_t::Jan, 31),
+                          toml::local_time(12, 30, 45)));
 
     v1 = toml::local_datetime(
                 toml::local_date(2018, toml::month_t::Apr, 1),
@@ -420,11 +565,16 @@ BOOST_AUTO_TEST_CASE(test_value_local_datetime)
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::LocalDatetime);
     BOOST_CHECK(v1.is(toml::value_t::LocalDatetime));
     BOOST_CHECK(v1.is<toml::LocalDatetime>());
+    BOOST_CHECK(v1.is_local_datetime());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::LocalDatetime>(),
                       toml::local_datetime(
                           toml::local_date(2018, toml::month_t::Apr, 1),
                           toml::local_time(1, 15, 30)));
+    BOOST_CHECK_EQUAL(v1.as_local_datetime(),
+                      toml::local_datetime(
+                          toml::local_date(2018, toml::month_t::Apr, 1),
+                          toml::local_time(1, 15, 30)));
 
     toml::value v2(v1);
     BOOST_CHECK(v2 == v1);
@@ -432,17 +582,25 @@ BOOST_AUTO_TEST_CASE(test_value_local_datetime)
     BOOST_CHECK_EQUAL(v2.type(), toml::value_t::LocalDatetime);
     BOOST_CHECK(v2.is(toml::value_t::LocalDatetime));
     BOOST_CHECK(v2.is<toml::LocalDatetime>());
+    BOOST_CHECK(v2.is_local_datetime());
 
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::LocalDatetime>(),
                       toml::local_datetime(
                           toml::local_date(2018, toml::month_t::Apr, 1),
                           toml::local_time(1, 15, 30)));
+    BOOST_CHECK_EQUAL(v2.as_local_datetime(),
+                      toml::local_datetime(
+                          toml::local_date(2018, toml::month_t::Apr, 1),
+                          toml::local_time(1, 15, 30)));
+
 
     v1 = true;
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Boolean);
     BOOST_CHECK(v1.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
 }
 
 BOOST_AUTO_TEST_CASE(test_value_offset_datetime)
@@ -456,6 +614,7 @@ BOOST_AUTO_TEST_CASE(test_value_offset_datetime)
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::OffsetDatetime);
     BOOST_CHECK(v1.is(toml::value_t::OffsetDatetime));
     BOOST_CHECK(v1.is<toml::OffsetDatetime>());
+    BOOST_CHECK(v1.is_offset_datetime());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::OffsetDatetime>(),
             toml::offset_datetime(
@@ -463,6 +622,12 @@ BOOST_AUTO_TEST_CASE(test_value_offset_datetime)
                 toml::local_time(12, 30, 45),
                 toml::time_offset(9, 0)
                 ));
+    BOOST_CHECK_EQUAL(v1.as_offset_datetime(),
+            toml::offset_datetime(
+                toml::local_date(2018, toml::month_t::Jan, 31),
+                toml::local_time(12, 30, 45),
+                toml::time_offset(9, 0)
+                ));
 
     v1 = toml::offset_datetime(
                 toml::local_date(2018, toml::month_t::Apr, 1),
@@ -472,12 +637,19 @@ BOOST_AUTO_TEST_CASE(test_value_offset_datetime)
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::OffsetDatetime);
     BOOST_CHECK(v1.is(toml::value_t::OffsetDatetime));
     BOOST_CHECK(v1.is<toml::OffsetDatetime>());
+    BOOST_CHECK(v1.is_offset_datetime());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::OffsetDatetime>(),
             toml::offset_datetime(
                 toml::local_date(2018, toml::month_t::Apr, 1),
                 toml::local_time(1, 15, 30),
                 toml::time_offset(9, 0)));
+    BOOST_CHECK_EQUAL(v1.as_offset_datetime(),
+            toml::offset_datetime(
+                toml::local_date(2018, toml::month_t::Apr, 1),
+                toml::local_time(1, 15, 30),
+                toml::time_offset(9, 0)));
+
 
     toml::value v2(v1);
     BOOST_CHECK(v2 == v1);
@@ -485,17 +657,26 @@ BOOST_AUTO_TEST_CASE(test_value_offset_datetime)
     BOOST_CHECK_EQUAL(v2.type(), toml::value_t::OffsetDatetime);
     BOOST_CHECK(v2.is(toml::value_t::OffsetDatetime));
     BOOST_CHECK(v2.is<toml::OffsetDatetime>());
+    BOOST_CHECK(v2.is_offset_datetime());
 
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::OffsetDatetime>(),
             toml::offset_datetime(
                 toml::local_date(2018, toml::month_t::Apr, 1),
                 toml::local_time(1, 15, 30),
                 toml::time_offset(9, 0)));
+    BOOST_CHECK_EQUAL(v2.as_offset_datetime(),
+            toml::offset_datetime(
+                toml::local_date(2018, toml::month_t::Apr, 1),
+                toml::local_time(1, 15, 30),
+                toml::time_offset(9, 0)));
+
     v1 = true;
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Boolean);
     BOOST_CHECK(v1.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
 }
 
 BOOST_AUTO_TEST_CASE(test_value_array)
@@ -507,16 +688,24 @@ BOOST_AUTO_TEST_CASE(test_value_array)
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Array);
     BOOST_CHECK(v1.is(toml::value_t::Array));
     BOOST_CHECK(v1.is<toml::Array>());
+    BOOST_CHECK(v1.is_array());
 
     BOOST_CHECK_EQUAL(v2.type(), toml::value_t::Array);
     BOOST_CHECK(v2.is(toml::value_t::Array));
     BOOST_CHECK(v2.is<toml::Array>());
+    BOOST_CHECK(v2.is_array());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(0).cast<toml::value_t::Integer>(), 1);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(1).cast<toml::value_t::Integer>(), 2);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(2).cast<toml::value_t::Integer>(), 3);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(3).cast<toml::value_t::Integer>(), 4);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(4).cast<toml::value_t::Integer>(), 5);
+    BOOST_CHECK_EQUAL(v1.as_array().at(0).as_integer(), 1);
+    BOOST_CHECK_EQUAL(v1.as_array().at(1).as_integer(), 2);
+    BOOST_CHECK_EQUAL(v1.as_array().at(2).as_integer(), 3);
+    BOOST_CHECK_EQUAL(v1.as_array().at(3).as_integer(), 4);
+    BOOST_CHECK_EQUAL(v1.as_array().at(4).as_integer(), 5);
+
 
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(0).cast<toml::value_t::Integer>(), 6);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(1).cast<toml::value_t::Integer>(), 7);
@@ -530,22 +719,36 @@ BOOST_AUTO_TEST_CASE(test_value_array)
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Array);
     BOOST_CHECK(v1.is(toml::value_t::Array));
     BOOST_CHECK(v1.is<toml::Array>());
+    BOOST_CHECK(v1.is_array());
 
     BOOST_CHECK_EQUAL(v2.type(), toml::value_t::Array);
     BOOST_CHECK(v2.is(toml::value_t::Array));
     BOOST_CHECK(v2.is<toml::Array>());
+    BOOST_CHECK(v2.is_array());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(0).cast<toml::value_t::Integer>(), 6);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(1).cast<toml::value_t::Integer>(), 7);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(2).cast<toml::value_t::Integer>(), 8);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(3).cast<toml::value_t::Integer>(), 9);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Array>().at(4).cast<toml::value_t::Integer>(), 0);
+    BOOST_CHECK_EQUAL(v1.as_array().at(0).as_integer(), 6);
+    BOOST_CHECK_EQUAL(v1.as_array().at(1).as_integer(), 7);
+    BOOST_CHECK_EQUAL(v1.as_array().at(2).as_integer(), 8);
+    BOOST_CHECK_EQUAL(v1.as_array().at(3).as_integer(), 9);
+    BOOST_CHECK_EQUAL(v1.as_array().at(4).as_integer(), 0);
+
 
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(0).cast<toml::value_t::Integer>(), 1);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(1).cast<toml::value_t::Integer>(), 2);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(2).cast<toml::value_t::Integer>(), 3);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(3).cast<toml::value_t::Integer>(), 4);
     BOOST_CHECK_EQUAL(v2.cast<toml::value_t::Array>().at(4).cast<toml::value_t::Integer>(), 5);
+    BOOST_CHECK_EQUAL(v2.as_array().at(0).as_integer(), 1);
+    BOOST_CHECK_EQUAL(v2.as_array().at(1).as_integer(), 2);
+    BOOST_CHECK_EQUAL(v2.as_array().at(2).as_integer(), 3);
+    BOOST_CHECK_EQUAL(v2.as_array().at(3).as_integer(), 4);
+    BOOST_CHECK_EQUAL(v2.as_array().at(4).as_integer(), 5);
+
 
     toml::value v3(v1);
     BOOST_CHECK(v3 == v1);
@@ -553,18 +756,27 @@ BOOST_AUTO_TEST_CASE(test_value_array)
     BOOST_CHECK_EQUAL(v3.type(), toml::value_t::Array);
     BOOST_CHECK(v3.is(toml::value_t::Array));
     BOOST_CHECK(v3.is<toml::Array>());
+    BOOST_CHECK(v3.is_array());
 
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Array>().at(0).cast<toml::value_t::Integer>(), 6);
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Array>().at(1).cast<toml::value_t::Integer>(), 7);
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Array>().at(2).cast<toml::value_t::Integer>(), 8);
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Array>().at(3).cast<toml::value_t::Integer>(), 9);
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Array>().at(4).cast<toml::value_t::Integer>(), 0);
+    BOOST_CHECK_EQUAL(v3.as_array().at(0).as_integer(), 6);
+    BOOST_CHECK_EQUAL(v3.as_array().at(1).as_integer(), 7);
+    BOOST_CHECK_EQUAL(v3.as_array().at(2).as_integer(), 8);
+    BOOST_CHECK_EQUAL(v3.as_array().at(3).as_integer(), 9);
+    BOOST_CHECK_EQUAL(v3.as_array().at(4).as_integer(), 0);
+
 
     v1 = true;
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Boolean);
     BOOST_CHECK(v1.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
 }
 
 BOOST_AUTO_TEST_CASE(test_value_table)
@@ -574,20 +786,30 @@ BOOST_AUTO_TEST_CASE(test_value_table)
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Table);
     BOOST_CHECK(v1.is(toml::value_t::Table));
     BOOST_CHECK(v1.is<toml::Table>());
+    BOOST_CHECK(v1.is_table());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("foo").cast<toml::value_t::Integer>(),    42);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("bar").cast<toml::value_t::Float>(),      3.14);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("baz").cast<toml::value_t::String>().str, "qux");
+    BOOST_CHECK_EQUAL(v1.as_table().at("foo").as_integer(),    42);
+    BOOST_CHECK_EQUAL(v1.as_table().at("bar").as_float(),   3.14);
+    BOOST_CHECK_EQUAL(v1.as_table().at("baz").as_string().str, "qux");
+
 
     v1 = toml::table{{"foo", 2.71}, {"bar", 54}, {"baz", "quux"}};
 
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Table);
     BOOST_CHECK(v1.is(toml::value_t::Table));
     BOOST_CHECK(v1.is<toml::Table>());
+    BOOST_CHECK(v1.is_table());
 
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("foo").cast<toml::value_t::Float>(),      2.71);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("bar").cast<toml::value_t::Integer>(),    54);
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Table>().at("baz").cast<toml::value_t::String>().str, "quux");
+    BOOST_CHECK_EQUAL(v1.as_table().at("foo").as_float(),   2.71);
+    BOOST_CHECK_EQUAL(v1.as_table().at("bar").as_integer(),    54);
+    BOOST_CHECK_EQUAL(v1.as_table().at("baz").as_string().str, "quux");
+
 
     toml::value v3(v1);
     BOOST_CHECK(v3 == v1);
@@ -595,14 +817,28 @@ BOOST_AUTO_TEST_CASE(test_value_table)
     BOOST_CHECK_EQUAL(v3.type(), toml::value_t::Table);
     BOOST_CHECK(v3.is(toml::value_t::Table));
     BOOST_CHECK(v3.is<toml::Table>());
+    BOOST_CHECK(v3.is_table());
 
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Table>().at("foo").cast<toml::value_t::Float>(),      2.71);
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Table>().at("bar").cast<toml::value_t::Integer>(),    54);
     BOOST_CHECK_EQUAL(v3.cast<toml::value_t::Table>().at("baz").cast<toml::value_t::String>().str, "quux");
+    BOOST_CHECK_EQUAL(v3.as_table().at("foo").as_float(),   2.71);
+    BOOST_CHECK_EQUAL(v3.as_table().at("bar").as_integer(),    54);
+    BOOST_CHECK_EQUAL(v3.as_table().at("baz").as_string().str, "quux");
+
 
     v1 = true;
     BOOST_CHECK_EQUAL(v1.type(), toml::value_t::Boolean);
     BOOST_CHECK(v1.is(toml::value_t::Boolean));
     BOOST_CHECK(v1.is<toml::Boolean>());
+    BOOST_CHECK(v1.is_boolean());
     BOOST_CHECK_EQUAL(v1.cast<toml::value_t::Boolean>(), true);
+    BOOST_CHECK_EQUAL(v1.as_boolean(), true);
+}
+
+BOOST_AUTO_TEST_CASE(test_value_empty)
+{
+    toml::value v1;
+    BOOST_CHECK(v1.is_uninitialized());
+    BOOST_CHECK(v1.is(toml::value_t::Empty));
 }

toml.hpp

@@ -34,8 +34,8 @@
 #endif
 
 #include "toml/parser.hpp"
+#include "toml/literal.hpp"
 #include "toml/serializer.hpp"
-#include "toml/to_toml.hpp"
 #include "toml/from_toml.hpp"
 #include "toml/get.hpp"
 

toml/combinator.hpp

@@ -9,7 +9,10 @@
 #include <type_traits>
 #include <iterator>
 #include <limits>
+#include <array>
 #include <iomanip>
+#include <cstdio>
+#include <cassert>
 #include <cctype>
 
 // they scans characters and returns region if it matches to the condition.
@@ -38,10 +41,12 @@ inline std::string show_char(const char c)
     }
     else
     {
-        std::ostringstream oss;
+        std::array<char, 5> buf;
-        oss << "0x" << std::hex << std::setfill('0') << std::setw(2)
+        buf.fill('\0');
-            << static_cast<int>(c);
+        const auto r = std::snprintf(
-        return oss.str();
+                buf.data(), buf.size(), "0x%02x", static_cast<int>(c) & 0xFF);
+        assert(r == buf.size() - 1);
+        return std::string(buf.data());
     }
 }
 
@@ -51,7 +56,8 @@ struct character
     static constexpr char target = C;
 
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         static_assert(std::is_same<char, typename Cont::value_type>::value,
                       "internal error: container::value_type should be `char`.");
@@ -61,11 +67,15 @@ struct character
 
         const char c = *(loc.iter());
         if(c != target)
+        {
+            if(msg)
             {
                 return err(concat_to_string("expected '", show_char(target),
                                             "' but got '", show_char(c), "'."));
             }
-        ++(loc.iter()); // update location
+            return err("");
+        }
+        loc.advance(); // update location
 
         return ok(region<Cont>(loc, first, loc.iter()));
     }
@@ -86,7 +96,8 @@ struct in_range
     static constexpr char lower = Low;
 
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         static_assert(std::is_same<char, typename Cont::value_type>::value,
                       "internal error: container::value_type should be `char`.");
@@ -96,13 +107,17 @@ struct in_range
 
         const char c = *(loc.iter());
         if(c < lower || upper < c)
+        {
+            if(msg)
             {
                 return err(concat_to_string("expected character in range "
                     "[", show_char(lower), ", ", show_char(upper), "] but got ",
                     "'", show_char(c), "'."));
             }
+            return err("");
+        }
 
-        ++(loc.iter());
+        loc.advance();
         return ok(region<Cont>(loc, first, loc.iter()));
     }
 
@@ -120,7 +135,8 @@ template<typename Combinator>
 struct exclude
 {
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         static_assert(std::is_same<char, typename Cont::value_type>::value,
                       "internal error: container::value_type should be `char`.");
@@ -128,15 +144,18 @@ struct exclude
         if(loc.iter() == loc.end()) {return err("not sufficient characters");}
         auto first = loc.iter();
 
-        auto rslt = Combinator::invoke(loc);
+        auto rslt = Combinator::invoke(loc, msg);
         if(rslt.is_ok())
         {
-            loc.iter() = first; // rollback
+            loc.reset(first);
-            return err(concat_to_string(
+            if(msg)
-                "invalid pattern (", Combinator::pattern(), ") appeared ",
+            {
-                rslt.unwrap().str()));
+                return err(concat_to_string("invalid pattern (",
+                    Combinator::pattern(), ") appeared ", rslt.unwrap().str()));
             }
-        loc.iter() = std::next(first);
+            return err("");
+        }
+        loc.reset(std::next(first)); // XXX maybe loc.advance() is okay but...
         return ok(region<Cont>(loc, first, loc.iter()));
     }
 
@@ -151,12 +170,13 @@ template<typename Combinator>
 struct maybe
 {
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         static_assert(std::is_same<char, typename Cont::value_type>::value,
                       "internal error: container::value_type should be `char`.");
 
-        const auto rslt = Combinator::invoke(loc);
+        const auto rslt = Combinator::invoke(loc, msg);
         if(rslt.is_ok())
         {
             return rslt;
@@ -177,34 +197,36 @@ template<typename Head, typename ... Tail>
 struct sequence<Head, Tail...>
 {
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         static_assert(std::is_same<char, typename Cont::value_type>::value,
                       "internal error: container::value_type should be `char`.");
 
         const auto first = loc.iter();
-        const auto rslt = Head::invoke(loc);
+        const auto rslt = Head::invoke(loc, msg);
         if(rslt.is_err())
         {
-            loc.iter() = first;
+            loc.reset(first);
             return err(rslt.unwrap_err());
         }
-        return sequence<Tail...>::invoke(loc, std::move(rslt.unwrap()), first);
+        return sequence<Tail...>::invoke(loc, std::move(rslt.unwrap()), first, msg);
     }
 
     // called from the above function only, recursively.
     template<typename Cont, typename Iterator>
     static result<region<Cont>, std::string>
-    invoke(location<Cont>& loc, region<Cont> reg, Iterator first)
+    invoke(location<Cont>& loc, region<Cont> reg, Iterator first,
+           const bool msg = false)
     {
-        const auto rslt = Head::invoke(loc);
+        const auto rslt = Head::invoke(loc, msg);
         if(rslt.is_err())
         {
-            loc.iter() = first;
+            loc.reset(first);
             return err(rslt.unwrap_err());
         }
         reg += rslt.unwrap(); // concat regions
-        return sequence<Tail...>::invoke(loc, std::move(reg), first);
+        return sequence<Tail...>::invoke(loc, std::move(reg), first, msg);
     }
 
     static std::string pattern()
@@ -219,12 +241,13 @@ struct sequence<Head>
     // would be called from sequence<T ...>::invoke only.
     template<typename Cont, typename Iterator>
     static result<region<Cont>, std::string>
-    invoke(location<Cont>& loc, region<Cont> reg, Iterator first)
+    invoke(location<Cont>& loc, region<Cont> reg, Iterator first,
+           const bool msg = false)
     {
-        const auto rslt = Head::invoke(loc);
+        const auto rslt = Head::invoke(loc, msg);
         if(rslt.is_err())
         {
-            loc.iter() = first;
+            loc.reset(first);
             return err(rslt.unwrap_err());
         }
         reg += rslt.unwrap(); // concat regions
@@ -240,14 +263,15 @@ template<typename Head, typename ... Tail>
 struct either<Head, Tail...>
 {
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         static_assert(std::is_same<char, typename Cont::value_type>::value,
                       "internal error: container::value_type should be `char`.");
 
-        const auto rslt = Head::invoke(loc);
+        const auto rslt = Head::invoke(loc, msg);
         if(rslt.is_ok()) {return rslt;}
-        return either<Tail...>::invoke(loc);
+        return either<Tail...>::invoke(loc, msg);
     }
 
     static std::string pattern()
@@ -259,11 +283,12 @@ template<typename Head>
 struct either<Head>
 {
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         static_assert(std::is_same<char, typename Cont::value_type>::value,
                       "internal error: container::value_type should be `char`.");
-        return Head::invoke(loc);
+        return Head::invoke(loc, msg);
     }
     static std::string pattern()
     {
@@ -282,16 +307,17 @@ template<typename T, std::size_t N>
 struct repeat<T, exactly<N>>
 {
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         region<Cont> retval(loc);
         const auto first = loc.iter();
         for(std::size_t i=0; i<N; ++i)
         {
-            auto rslt = T::invoke(loc);
+            auto rslt = T::invoke(loc, msg);
             if(rslt.is_err())
             {
-                loc.iter() = first;
+                loc.reset(first);
                 return err(rslt.unwrap_err());
             }
             retval += rslt.unwrap();
@@ -308,24 +334,25 @@ template<typename T, std::size_t N>
 struct repeat<T, at_least<N>>
 {
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         region<Cont> retval(loc);
 
         const auto first = loc.iter();
         for(std::size_t i=0; i<N; ++i)
         {
-            auto rslt = T::invoke(loc);
+            auto rslt = T::invoke(loc, msg);
             if(rslt.is_err())
             {
-                loc.iter() = first;
+                loc.reset(first);
                 return err(rslt.unwrap_err());
             }
             retval += rslt.unwrap();
         }
         while(true)
         {
-            auto rslt = T::invoke(loc);
+            auto rslt = T::invoke(loc, msg);
             if(rslt.is_err())
             {
                 return ok(std::move(retval));
@@ -343,12 +370,13 @@ template<typename T>
 struct repeat<T, unlimited>
 {
     template<typename Cont>
-    static result<region<Cont>, std::string> invoke(location<Cont>& loc)
+    static result<region<Cont>, std::string>
+    invoke(location<Cont>& loc, const bool msg = false)
     {
         region<Cont> retval(loc);
         while(true)
         {
-            auto rslt = T::invoke(loc);
+            auto rslt = T::invoke(loc, msg);
             if(rslt.is_err())
             {
                 return ok(std::move(retval));

toml/datetime.hpp

@@ -1,7 +1,7 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_DATETIME
+#ifndef TOML11_DATETIME_HPP
-#define TOML11_DATETIME
+#define TOML11_DATETIME_HPP
 #include <chrono>
 #include <tuple>
 #include <array>
@@ -25,16 +25,18 @@ inline std::tm localtime_s(const std::time_t* src)
 {
     std::tm dst;
     const auto result = ::localtime_r(src, &dst);
-    if(!result)
+    if (!result) { throw std::runtime_error("localtime_r failed."); }
-    {
+    return dst;
-        throw std::runtime_error("localtime_r failed.");
 }
+#elif _MSC_VER
+inline std::tm localtime_s(const std::time_t* src)
+{
+    std::tm dst;
+    const auto result = ::localtime_s(&dst, src);
+    if (result) { throw std::runtime_error("localtime_s failed."); }
     return dst;
 }
 #else
-// XXX: On Windows, std::localtime is thread-safe because they uses thread-local
-// storage to store the instance of std::tm. On the other platforms, it may not
-// be thread-safe.
 inline std::tm localtime_s(const std::time_t* src)
 {
     const auto result = std::localtime(src);
@@ -332,17 +334,10 @@ operator<<(std::basic_ostream<charT, traits>& os, const time_offset& offset)
         os << 'Z';
         return os;
     }
-    if(static_cast<int>(offset.hour) * static_cast<int>(offset.minute) < 0)
+    int minute = static_cast<int>(offset.hour) * 60 + offset.minute;
-    {
+    if(minute < 0){os << '-'; minute = std::abs(minute);} else {os << '+';}
-        const int min = static_cast<int>(offset.hour) * 60 + offset.minute;
+    os << std::setfill('0') << std::setw(2) << minute / 60 << ':';
-        if(min < 0){os << '-';} else {os << '+';}
+    os << std::setfill('0') << std::setw(2) << minute % 60;
-        os << std::setfill('0') << std::setw(2) << min / 60 << ':';
-        os << std::setfill('0') << std::setw(2) << min % 60;
-        return os;
-    }
-    if(offset.hour < 0){os << '-';} else {os << '+';}
-    os << std::setfill('0') << std::setw(2) << static_cast<int>(offset.hour) << ':';
-    os << std::setfill('0') << std::setw(2) << static_cast<int>(offset.minute);
     return os;
 }
 
@@ -367,12 +362,12 @@ struct local_datetime
         // can be used to get millisecond & microsecond information.
         const auto t_diff = tp -
             std::chrono::system_clock::from_time_t(std::mktime(&time));
-        this->time.millisecond = std::chrono::duration_cast<
+        this->time.millisecond = static_cast<std::uint16_t>(
-            std::chrono::milliseconds>(t_diff).count();
+          std::chrono::duration_cast<std::chrono::milliseconds>(t_diff).count());
-        this->time.microsecond = std::chrono::duration_cast<
+        this->time.microsecond = static_cast<std::uint16_t>(
-            std::chrono::microseconds>(t_diff).count();
+          std::chrono::duration_cast<std::chrono::microseconds>(t_diff).count());
-        this->time.nanosecond = std::chrono::duration_cast<
+        this->time.nanosecond = static_cast<std::uint16_t>(
-            std::chrono::nanoseconds >(t_diff).count();
+          std::chrono::duration_cast<std::chrono::nanoseconds >(t_diff).count());
     }
 
     explicit local_datetime(const std::time_t t)

toml/exception.hpp

@@ -1,7 +1,7 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_EXCEPTION
+#ifndef TOML11_EXCEPTION_HPP
-#define TOML11_EXCEPTION
+#define TOML11_EXCEPTION_HPP
 #include <stdexcept>
 #include <string>
 

toml/from.hpp

@@ -0,0 +1,20 @@
+//     Copyright Toru Niina 2019.
+// Distributed under the MIT License.
+#ifndef TOML11_FROM_HPP
+#define TOML11_FROM_HPP
+#include "traits.hpp"
+
+namespace toml
+{
+
+template<typename T>
+struct from;
+// {
+//     static T from_toml(const toml::value& v)
+//     {
+//         // User-defined conversions ...
+//     }
+// };
+
+} // toml
+#endif // TOML11_FROM_HPP

toml/from_toml.hpp

@@ -1,7 +1,7 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_FROM_TOML
+#ifndef TOML11_FROM_TOML_HPP
-#define TOML11_FROM_TOML
+#define TOML11_FROM_TOML_HPP
 #include "get.hpp"
 
 namespace toml
@@ -51,7 +51,7 @@ struct from_toml_tie_impl
 template<typename ... Ts>
 struct from_toml_tie_impl<0, Ts...>
 {
-    static void invoke(std::tuple<Ts& ...> tie, const toml::value& v)
+    static void invoke(std::tuple<Ts& ...>, const toml::value&)
     {
         return;
     }

toml/get.hpp

@@ -1,7 +1,8 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_GET
+#ifndef TOML11_GET_HPP
-#define TOML11_GET
+#define TOML11_GET_HPP
+#include "from.hpp"
 #include "result.hpp"
 #include "value.hpp"
 #include <algorithm>
@@ -107,12 +108,24 @@ inline std::string get(value&& v)
     return std::move(v.cast<value_t::String>().str);
 }
 
+// ============================================================================
+// std::string_view
+
+#if __cplusplus >= 201703L
+template<typename T, typename std::enable_if<
+    std::is_same<T, std::string_view>::value, std::nullptr_t>::type = nullptr>
+inline std::string_view get(const value& v)
+{
+    return std::string_view(v.cast<value_t::String>().str);
+}
+#endif
+
 // ============================================================================
 // std::chrono::duration from toml::local_time.
 
 template<typename T, typename std::enable_if<
     detail::is_chrono_duration<T>::value, std::nullptr_t>::type = nullptr>
-inline T get(value& v)
+inline T get(const value& v)
 {
     return std::chrono::duration_cast<T>(
             std::chrono::nanoseconds(v.cast<value_t::LocalTime>()));
@@ -124,7 +137,7 @@ inline T get(value& v)
 template<typename T, typename std::enable_if<
     std::is_same<std::chrono::system_clock::time_point, T>::value,
     std::nullptr_t>::type = nullptr>
-inline T get(value& v)
+inline T get(const value& v)
 {
     switch(v.type())
     {
@@ -173,6 +186,20 @@ template<typename T, typename std::enable_if<detail::conjunction<
     >::value, std::nullptr_t>::type = nullptr>
 T get(const toml::value& v);
 
+template<typename T, typename std::enable_if<detail::conjunction<
+    detail::negation<detail::is_exact_toml_type<T>>, // not a toml::value
+    detail::has_from_toml_method<T>, // but has from_toml(toml::value) memfn
+    std::is_default_constructible<T> // and default constructible
+    >::value, std::nullptr_t>::type = nullptr>
+T get(const toml::value& v);
+
+template<typename T, typename std::enable_if<detail::conjunction<
+    detail::negation<detail::is_exact_toml_type<T>> // not a toml::value
+    >::value, std::nullptr_t>::type = nullptr,
+    std::size_t = sizeof(::toml::from<T>) // and has from<T> specialization
+    >
+T get(const toml::value& v);
+
 // ============================================================================
 // array-like types; most likely STL container, like std::vector, etc.
 
@@ -297,6 +324,29 @@ T get(const toml::value& v)
     return map;
 }
 
+
+// ============================================================================
+// user-defined, but compatible types.
+
+template<typename T, typename std::enable_if<detail::conjunction<
+    detail::negation<detail::is_exact_toml_type<T>>, // not a toml::value
+    detail::has_from_toml_method<T>, // but has from_toml(toml::value) memfn
+    std::is_default_constructible<T> // and default constructible
+    >::value, std::nullptr_t>::type>
+T get(const toml::value& v)
+{
+    T ud;
+    ud.from_toml(v);
+    return ud;
+}
+template<typename T, typename std::enable_if<detail::conjunction<
+    detail::negation<detail::is_exact_toml_type<T>> // not a toml::value
+    >::value, std::nullptr_t>::type, std::size_t>   // and has from<T>
+T get(const toml::value& v)
+{
+    return ::toml::from<T>::from_toml(v);
+}
+
 // ============================================================================
 // find and get
 
@@ -382,13 +432,14 @@ find(toml::value&& v, const toml::key& ky)
 
 
 // ============================================================================
-// get_or
+// get_or(value, fallback)
 
-template<typename T>
+// ----------------------------------------------------------------------------
-decltype(::toml::get<typename std::remove_cv<
+// specialization for the exact toml types (return type becomes lvalue ref)
-            typename std::remove_reference<T>::type>::type>(
+
-        std::declval<const toml::value&>()))
+template<typename T, typename std::enable_if<
-get_or(const toml::value& v, T&& opt)
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
+T const& get_or(const toml::value& v, const T& opt)
 {
     try
     {
@@ -397,14 +448,12 @@ get_or(const toml::value& v, T&& opt)
     }
     catch(...)
     {
-        return std::forward<T>(opt);
+        return opt;
     }
 }
-template<typename T>
+template<typename T, typename std::enable_if<
-decltype(::toml::get<typename std::remove_cv<
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
-            typename std::remove_reference<T>::type>::type>(
+T& get_or(toml::value& v, T& opt)
-        std::declval<toml::value&>()))
-get_or(toml::value& v, T&& opt)
 {
     try
     {
@@ -413,75 +462,270 @@ get_or(toml::value& v, T&& opt)
     }
     catch(...)
     {
-        return std::forward<T>(opt);
+        return opt;
     }
 }
-template<typename T>
+template<typename T, typename std::enable_if<
-decltype(::toml::get<typename std::remove_cv<
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
-            typename std::remove_reference<T>::type>::type>(
+T&& get_or(toml::value&& v, T&& opt)
-        std::declval<toml::value&&>()))
-get_or(toml::value&& v, T&& opt)
 {
     try
     {
         return get<typename std::remove_cv<
-            typename std::remove_reference<T>::type>::type>(std::move(v));
+            typename std::remove_reference<T>::type>::type>(v);
     }
     catch(...)
     {
-        return std::forward<T>(opt);
+        return opt;
     }
 }
 
+// ----------------------------------------------------------------------------
+// specialization for std::string (return type becomes lvalue ref)
 
-template<typename T>
+template<typename T, typename std::enable_if<
-auto get_or(const toml::table& tab, const toml::key& ky, T&& opt)
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
-    -> decltype(get_or(std::declval<value const&>(), std::forward<T>(opt)))
+std::string const& get_or(const toml::value& v, const T& opt)
 {
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
+    try
-    return ::toml::get_or(tab.at(ky), std::forward<T>(opt));
+    {
+        return get<std::string>(v);
     }
-template<typename T>
+    catch(...)
-auto get_or(toml::table& tab, const toml::key& ky, T&& opt)
-    -> decltype(get_or(std::declval<value&>(), std::forward<T>(opt)))
     {
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
+        return opt;
-    return ::toml::get_or(tab[ky], std::forward<T>(opt));
     }
-template<typename T>
+}
-auto get_or(toml::table&& tab, const toml::key& ky, T&& opt)
+template<typename T, typename std::enable_if<
-    -> decltype(get_or(std::declval<value&&>(), std::forward<T>(opt)))
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
+std::string& get_or(toml::value& v, T& opt)
 {
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
+    try
-    return ::toml::get_or(std::move(tab[ky]), std::forward<T>(opt));
+    {
+        return get<std::string>(v);
+    }
+    catch(...)
+    {
+        return opt;
+    }
+}
+template<typename T, typename std::enable_if<
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
+std::string get_or(toml::value&& v, T&& opt)
+{
+    try
+    {
+        return get<std::string>(v);
+    }
+    catch(...)
+    {
+        return opt;
+    }
+}
+template<typename T, typename std::enable_if<
+    detail::is_string_literal<typename std::remove_reference<T>::type>::value,
+    std::nullptr_t>::type = nullptr>
+std::string get_or(const toml::value& v, T&& opt)
+{
+    try
+    {
+        return get<std::string>(v);
+    }
+    catch(...)
+    {
+        return std::string(opt);
+    }
 }
 
-template<typename T>
+// ----------------------------------------------------------------------------
-auto get_or(const toml::value& v, const toml::key& ky, T&& opt)
+// others (require type conversion and return type cannot be lvalue reference)
-    -> decltype(get_or(std::declval<value const&>(), std::forward<T>(opt)))
+
+template<typename T, typename std::enable_if<detail::conjunction<
+    detail::negation<detail::is_exact_toml_type<T>>,
+    detail::negation<std::is_same<T, std::string>>,
+    detail::negation<detail::is_string_literal<typename std::remove_reference<T>::type>>
+    >::value, std::nullptr_t>::type = nullptr>
+T get_or(const toml::value& v, T&& opt)
 {
-    if(v.type() != toml::value_t::Table){return std::forward<T>(opt);}
+    try
+    {
+        return get<typename std::remove_cv<
+            typename std::remove_reference<T>::type>::type>(v);
+    }
+    catch(...)
+    {
+        return opt;
+    }
+}
+
+// ===========================================================================
+// find_or(value, key, fallback)
+
+// ---------------------------------------------------------------------------
+// exact types (return type can be a reference)
+template<typename T, typename std::enable_if<
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
+T const& find_or(const toml::value& v, const toml::key& ky, const T& opt)
+{
+    if(!v.is_table()) {return opt;}
     const auto& tab = toml::get<toml::table>(v);
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
+    if(tab.count(ky) == 0) {return opt;}
-    return ::toml::get_or(tab.at(ky), std::forward<T>(opt));
+    return get_or(tab.at(ky), opt);
 }
-template<typename T>
+
-auto get_or(toml::value& v, const toml::key& ky, T&& opt)
+template<typename T, typename std::enable_if<
-    -> decltype(get_or(std::declval<value&>(), std::forward<T>(opt)))
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
+T& find_or(toml::value& v, const toml::key& ky, T& opt)
 {
-    if(v.type() != toml::value_t::Table){return std::forward<T>(opt);}
+    if(!v.is_table()) {return opt;}
     auto& tab = toml::get<toml::table>(v);
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
+    if(tab.count(ky) == 0) {return opt;}
-    return ::toml::get_or(tab[ky], std::forward<T>(opt));
+    return get_or(tab[ky], opt);
 }
-template<typename T>
+
-auto get_or(toml::value&& v, const toml::key& ky, T&& opt)
+template<typename T, typename std::enable_if<
-    -> decltype(get_or(std::declval<value&&>(), std::forward<T>(opt)))
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
+T&& find_or(toml::value&& v, const toml::key& ky, T&& opt)
 {
-    if(v.type() != toml::value_t::Table){return std::forward<T>(opt);}
+    if(!v.is_table()) {return opt;}
     auto tab = toml::get<toml::table>(std::move(v));
-    if(tab.count(ky) == 0) {return std::forward<T>(opt);}
+    if(tab.count(ky) == 0) {return opt;}
-    return ::toml::get_or(std::move(tab[ky]), std::forward<T>(opt));
+    return get_or(std::move(tab[ky]), std::forward<T>(opt));
+}
+
+// ---------------------------------------------------------------------------
+// std::string (return type can be a reference)
+template<typename T, typename std::enable_if<
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
+std::string const& find_or(const toml::value& v, const toml::key& ky, const T& opt)
+{
+    if(!v.is_table()) {return opt;}
+    const auto& tab = toml::get<toml::table>(v);
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(tab.at(ky), opt);
+}
+template<typename T, typename std::enable_if<
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
+std::string& find_or(toml::value& v, const toml::key& ky, T& opt)
+{
+    if(!v.is_table()) {return opt;}
+    auto& tab = toml::get<toml::table>(v);
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(tab[ky], opt);
+}
+template<typename T, typename std::enable_if<
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
+std::string find_or(toml::value&& v, const toml::key& ky, T&& opt)
+{
+    if(!v.is_table()) {return opt;}
+    auto tab = toml::get<toml::table>(std::move(v));
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(std::move(tab[ky]), std::forward<T>(opt));
+}
+
+// ---------------------------------------------------------------------------
+// string literal (deduced as std::string)
+template<typename T, typename std::enable_if<
+    detail::is_string_literal<typename std::remove_reference<T>::type>::value,
+    std::nullptr_t>::type = nullptr>
+std::string find_or(const toml::value& v, const toml::key& ky, T&& opt)
+{
+    if(!v.is_table()) {return opt;}
+    const auto& tab = toml::get<toml::table>(v);
+    if(tab.count(ky) == 0) {return std::string(opt);}
+    return get_or(tab.at(ky), std::forward<T>(opt));
+}
+
+// ---------------------------------------------------------------------------
+// others (require type conversion and return type cannot be lvalue reference)
+template<typename T, typename std::enable_if<detail::conjunction<
+    detail::negation<detail::is_exact_toml_type<T>>,
+    detail::negation<std::is_same<T, std::string>>,
+    detail::negation<detail::is_string_literal<typename std::remove_reference<T>::type>>
+    >::value, std::nullptr_t>::type = nullptr>
+T find_or(const toml::value& v, const toml::key& ky, T&& opt)
+{
+    if(!v.is_table()) {return opt;}
+    const auto& tab = toml::get<toml::table>(v);
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(tab.at(ky), std::forward<T>(opt));
+}
+
+// ===========================================================================
+// find_or(table, key, opt)
+
+// ---------------------------------------------------------------------------
+// exact types (return type can be a reference)
+template<typename T, typename std::enable_if<
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
+T const& find_or(const toml::table& tab, const toml::key& ky, const T& opt)
+{
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(tab.at(ky), opt);
+}
+
+template<typename T, typename std::enable_if<
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
+T& find_or(toml::table& tab, const toml::key& ky, T& opt)
+{
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(tab[ky], opt);
+}
+
+template<typename T, typename std::enable_if<
+    detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
+T&& find_or(toml::table&& tab, const toml::key& ky, T&& opt)
+{
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(std::move(tab[ky]), std::forward<T>(opt));
+}
+
+// ---------------------------------------------------------------------------
+// std::string (return type can be a reference)
+template<typename T, typename std::enable_if<
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
+std::string const& find_or(const toml::table& tab, const toml::key& ky, const T& opt)
+{
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(tab.at(ky), opt);
+}
+template<typename T, typename std::enable_if<
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
+std::string& find_or(toml::table& tab, const toml::key& ky, T& opt)
+{
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(tab[ky], opt);
+}
+template<typename T, typename std::enable_if<
+    std::is_same<T, std::string>::value, std::nullptr_t>::type = nullptr>
+std::string find_or(toml::table&& tab, const toml::key& ky, T&& opt)
+{
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(std::move(tab[ky]), std::forward<T>(opt));
+}
+
+// ---------------------------------------------------------------------------
+// string literal (deduced as std::string)
+template<typename T, typename std::enable_if<
+    detail::is_string_literal<typename std::remove_reference<T>::type>::value,
+    std::nullptr_t>::type = nullptr>
+std::string find_or(const toml::table& tab, const toml::key& ky, T&& opt)
+{
+    if(tab.count(ky) == 0) {return std::string(opt);}
+    return get_or(tab.at(ky), std::forward<T>(opt));
+}
+
+// ---------------------------------------------------------------------------
+// others (require type conversion and return type cannot be lvalue reference)
+template<typename T, typename std::enable_if<detail::conjunction<
+    detail::negation<detail::is_exact_toml_type<T>>,
+    detail::negation<std::is_same<T, std::string>>,
+    detail::negation<detail::is_string_literal<typename std::remove_reference<T>::type>>
+    >::value, std::nullptr_t>::type = nullptr>
+T find_or(const toml::table& tab, const toml::key& ky, T&& opt)
+{
+    if(tab.count(ky) == 0) {return opt;}
+    return get_or(tab.at(ky), std::forward<T>(opt));
 }
 
 // ============================================================================

toml/into.hpp

@@ -0,0 +1,20 @@
+//     Copyright Toru Niina 2019.
+// Distributed under the MIT License.
+#ifndef TOML11_INTO_HPP
+#define TOML11_INTO_HPP
+#include "traits.hpp"
+
+namespace toml
+{
+
+template<typename T>
+struct into;
+// {
+//     static toml::value into_toml(const T& user_defined_type)
+//     {
+//         // User-defined conversions ...
+//     }
+// };
+
+} // toml
+#endif // TOML11_INTO_HPP

toml/literal.hpp

@@ -0,0 +1,91 @@
+//     Copyright Toru Niina 2019.
+// Distributed under the MIT License.
+#ifndef TOML11_LITERAL_HPP
+#define TOML11_LITERAL_HPP
+#include "parser.hpp"
+
+namespace toml
+{
+inline namespace literals
+{
+inline namespace toml_literals
+{
+
+inline ::toml::value operator""_toml(const char* str, std::size_t len)
+{
+    ::toml::detail::location<std::vector<char>>
+        loc(/* filename = */ std::string("TOML literal encoded in a C++ code"),
+            /* contents = */ std::vector<char>(str, str + len));
+
+    // if there are some comments or empty lines, skip them.
+    using skip_line = ::toml::detail::repeat<toml::detail::sequence<
+            ::toml::detail::maybe<::toml::detail::lex_ws>,
+            ::toml::detail::maybe<::toml::detail::lex_comment>,
+            ::toml::detail::lex_newline
+        >, ::toml::detail::at_least<1>>;
+    skip_line::invoke(loc);
+
+    // if there are some whitespaces before a value, skip them.
+    using skip_ws = ::toml::detail::repeat<
+        ::toml::detail::lex_ws, ::toml::detail::at_least<1>>;
+    skip_ws::invoke(loc);
+
+    // to distinguish arrays and tables, first check it is a table or not.
+    //
+    // "[1,2,3]"_toml;   // this is an array
+    // "[table]"_toml;   // a table that has an empty table named "table" inside.
+    // "[[1,2,3]]"_toml; // this is an array of arrays
+    // "[[table]]"_toml; // this is a table that has an array of tables inside.
+    //
+    // "[[1]]"_toml;     // this can be both... (currently it becomes a table)
+    // "1 = [{}]"_toml;  // this is a table that has an array of table named 1.
+    // "[[1,]]"_toml;    // this is an array of arrays.
+    // "[[1],]"_toml;    // this also.
+
+    const auto the_front = loc.iter();
+
+    const bool is_table_key = ::toml::detail::lex_std_table::invoke(loc);
+    loc.reset(the_front);
+
+    const bool is_aots_key  = ::toml::detail::lex_array_table::invoke(loc);
+    loc.reset(the_front);
+
+    // If it is neither a table-key or a array-of-table-key, it may be a value.
+    if(!is_table_key && !is_aots_key)
+    {
+        if(auto data = ::toml::detail::parse_value(loc))
+        {
+            return data.unwrap();
+        }
+    }
+
+    // Note that still it can be a table, because the literal might be something
+    // like the following.
+    // ```cpp
+    // R"( // c++11 raw string literals
+    //   key = "value"
+    //   int = 42
+    // )"_toml;
+    // ```
+    // It is a valid toml file.
+    // It should be parsed as if we parse a file with this content.
+
+    if(auto data = ::toml::detail::parse_toml_file(loc))
+    {
+        loc.reset(loc.begin()); // rollback to the top of the literal
+        // skip needless characters for error message
+        skip_line::invoke(loc); // skip the first several needless lines
+        skip_ws::invoke(loc);   // skip the first several needless whitespaces
+        return ::toml::value(std::move(data.unwrap()),
+                ::toml::detail::region<std::vector<char>>(std::move(loc)));
+    }
+    else // none of them.
+    {
+        throw ::toml::syntax_error(data.unwrap_err());
+    }
+}
+
+} // toml_literals
+} // literals
+} // toml
+#endif//TOML11_LITERAL_HPP

toml/parser.hpp

@@ -33,7 +33,7 @@ parse_boolean(location<Container>& loc)
                 {{std::addressof(reg), "invalid token"}}));
         }
     }
-    loc.iter() = first; //rollback
+    loc.reset(first); //rollback
     return err(format_underline("[error] toml::parse_boolean: ",
                {{std::addressof(loc), "the next token is not a boolean"}}));
 }
@@ -62,7 +62,7 @@ parse_binary_integer(location<Container>& loc)
         }
         return ok(std::make_pair(retval, token.unwrap()));
     }
-    loc.iter() = first;
+    loc.reset(first);
     return err(format_underline("[error] toml::parse_binary_integer:",
                {{std::addressof(loc), "the next token is not an integer"}}));
 }
@@ -83,7 +83,7 @@ parse_octal_integer(location<Container>& loc)
         iss >> std::oct >> retval;
         return ok(std::make_pair(retval, token.unwrap()));
     }
-    loc.iter() = first;
+    loc.reset(first);
     return err(format_underline("[error] toml::parse_octal_integer:",
                {{std::addressof(loc), "the next token is not an integer"}}));
 }
@@ -104,7 +104,7 @@ parse_hexadecimal_integer(location<Container>& loc)
         iss >> std::hex >> retval;
         return ok(std::make_pair(retval, token.unwrap()));
     }
-    loc.iter() = first;
+    loc.reset(first);
     return err(format_underline("[error] toml::parse_hexadecimal_integer",
                {{std::addressof(loc), "the next token is not an integer"}}));
 }
@@ -116,10 +116,28 @@ parse_integer(location<Container>& loc)
     const auto first = loc.iter();
     if(first != loc.end() && *first == '0')
     {
-        if(const auto bin = parse_binary_integer     (loc)) {return bin;}
+        const auto second = std::next(first);
-        if(const auto oct = parse_octal_integer      (loc)) {return oct;}
+        if(second == loc.end()) // the token is just zero.
-        if(const auto hex = parse_hexadecimal_integer(loc)) {return hex;}
+        {
-        // else, maybe just zero.
+            return ok(std::make_pair(0, region<Container>(loc, first, second)));
+        }
+
+        if(*second == 'b') {return parse_binary_integer     (loc);} // 0b1100
+        if(*second == 'o') {return parse_octal_integer      (loc);} // 0o775
+        if(*second == 'x') {return parse_hexadecimal_integer(loc);} // 0xC0FFEE
+
+        if(std::isdigit(*second))
+        {
+            return err(format_underline("[error] toml::parse_integer: "
+                "leading zero in an Integer is not allowed.",
+                {{std::addressof(loc), "leading zero"}}));
+        }
+        else if(std::isalpha(*second))
+        {
+             return err(format_underline("[error] toml::parse_integer: "
+                "unknown integer prefix appeared.",
+                {{std::addressof(loc), "none of 0x, 0o, 0b"}}));
+        }
     }
 
     if(const auto token = lex_dec_int::invoke(loc))
@@ -132,7 +150,7 @@ parse_integer(location<Container>& loc)
         iss >> retval;
         return ok(std::make_pair(retval, token.unwrap()));
     }
-    loc.iter() = first;
+    loc.reset(first);
     return err(format_underline("[error] toml::parse_integer: ",
                {{std::addressof(loc), "the next token is not an integer"}}));
 }
@@ -221,7 +239,7 @@ parse_floating(location<Container>& loc)
         iss >> v;
         return ok(std::make_pair(v, token.unwrap()));
     }
-    loc.iter() = first;
+    loc.reset(first);
     return err(format_underline("[error] toml::parse_floating: ",
                {{std::addressof(loc), "the next token is not a float"}}));
 }
@@ -250,11 +268,11 @@ std::string read_utf8_codepoint(const region<Container>& reg,
     {
         if(0xD800 <= codepoint && codepoint <= 0xDFFF)
         {
-            std::cerr << format_underline("[warning] "
+            throw syntax_error(format_underline("[error] "
                 "toml::read_utf8_codepoint: codepoints in the range "
                 "[0xD800, 0xDFFF] are not valid UTF-8.", {{
                     std::addressof(loc), "not a valid UTF-8 codepoint"
-                }}) << std::endl;
+                }}));
         }
         assert(codepoint < 0xD800 || 0xDFFF < codepoint);
         // 1110yyyy 10yxxxxx 10xxxxxx
@@ -262,15 +280,8 @@ std::string read_utf8_codepoint(const region<Container>& reg,
         character += static_cast<unsigned char>(0x80|(codepoint >> 6 & 0x3F));
         character += static_cast<unsigned char>(0x80|(codepoint      & 0x3F));
     }
-    else if(codepoint < 0x200000) // U+010000 ... U+1FFFFF
+    else if(codepoint < 0x110000) // U+010000 ... U+10FFFF
     {
-        if(0x10FFFF < codepoint) // out of Unicode region
-        {
-            std::cerr << format_underline("[error] "
-                "toml::read_utf8_codepoint: input codepoint is too large to "
-                "decode as a unicode character.", {{std::addressof(loc),
-                "should be in [0x00..0x10FFFF]"}}) << std::endl;
-        }
         // 11110yyy 10yyxxxx 10xxxxxx 10xxxxxx
         character += static_cast<unsigned char>(0xF0| codepoint >> 18);
         character += static_cast<unsigned char>(0x80|(codepoint >> 12 & 0x3F));
@@ -279,9 +290,9 @@ std::string read_utf8_codepoint(const region<Container>& reg,
     }
     else // out of UTF-8 region
     {
-        throw std::range_error(format_underline(concat_to_string("[error] "
+        throw syntax_error(format_underline("[error] toml::read_utf8_codepoint:"
-                "input codepoint (", str, ") is too large to encode as utf-8."),
+            " input codepoint is too large.",
-                {{std::addressof(reg), "should be in [0x00..0x10FFFF]"}}));
+            {{std::addressof(loc), "should be in [0x00..0x10FFFF]"}}));
     }
     return character;
 }
@@ -295,16 +306,16 @@ result<std::string, std::string> parse_escape_sequence(location<Container>& loc)
         return err(format_underline("[error]: toml::parse_escape_sequence: ", {{
             std::addressof(loc), "the next token is not a backslash \"\\\""}}));
     }
-    ++loc.iter();
+    loc.advance();
     switch(*loc.iter())
     {
-        case '\\':{++loc.iter(); return ok(std::string("\\"));}
+        case '\\':{loc.advance(); return ok(std::string("\\"));}
-        case '"' :{++loc.iter(); return ok(std::string("\""));}
+        case '"' :{loc.advance(); return ok(std::string("\""));}
-        case 'b' :{++loc.iter(); return ok(std::string("\b"));}
+        case 'b' :{loc.advance(); return ok(std::string("\b"));}
-        case 't' :{++loc.iter(); return ok(std::string("\t"));}
+        case 't' :{loc.advance(); return ok(std::string("\t"));}
-        case 'n' :{++loc.iter(); return ok(std::string("\n"));}
+        case 'n' :{loc.advance(); return ok(std::string("\n"));}
-        case 'f' :{++loc.iter(); return ok(std::string("\f"));}
+        case 'f' :{loc.advance(); return ok(std::string("\f"));}
-        case 'r' :{++loc.iter(); return ok(std::string("\r"));}
+        case 'r' :{loc.advance(); return ok(std::string("\r"));}
         case 'u' :
         {
             if(const auto token = lex_escape_unicode_short::invoke(loc))
@@ -315,7 +326,7 @@ result<std::string, std::string> parse_escape_sequence(location<Container>& loc)
             {
                 return err(format_underline("[error] parse_escape_sequence: "
                            "invalid token found in UTF-8 codepoint uXXXX.",
-                           {{std::addressof(loc), token.unwrap_err()}}));
+                           {{std::addressof(loc), "here"}}));
             }
         }
         case 'U':
@@ -328,7 +339,7 @@ result<std::string, std::string> parse_escape_sequence(location<Container>& loc)
             {
                 return err(format_underline("[error] parse_escape_sequence: "
                            "invalid token found in UTF-8 codepoint Uxxxxxxxx",
-                           {{std::addressof(loc), token.unwrap_err()}}));
+                           {{std::addressof(loc), "here"}}));
             }
         }
     }
@@ -338,7 +349,7 @@ result<std::string, std::string> parse_escape_sequence(location<Container>& loc)
            "escape sequence is one of \\, \", b, t, n, f, r, uxxxx, Uxxxxxxxx"}},
            /* Hints = */{"if you want to write backslash as just one backslash, "
            "use literal string like: regex    = '<\\i\\c*\\s*>'"});
-    loc.iter() = first;
+    loc.reset(first);
     return err(msg);
 }
 
@@ -350,7 +361,7 @@ parse_ml_basic_string(location<Container>& loc)
     if(const auto token = lex_ml_basic_string::invoke(loc))
     {
         auto inner_loc = loc;
-        inner_loc.iter() = first;
+        inner_loc.reset(first);
 
         std::string retval;
         retval.reserve(token.unwrap().size());
@@ -394,8 +405,10 @@ parse_ml_basic_string(location<Container>& loc)
     }
     else
     {
-        loc.iter() = first;
+        loc.reset(first);
-        return err(token.unwrap_err());
+        return err(format_underline("[error] toml::parse_ml_basic_string: "
+                   "the next token is not a multiline string",
+                   {{std::addressof(loc), "here"}}));
     }
 }
 
@@ -407,7 +420,7 @@ parse_basic_string(location<Container>& loc)
     if(const auto token = lex_basic_string::invoke(loc))
     {
         auto inner_loc = loc;
-        inner_loc.iter() = first;
+        inner_loc.reset(first);
 
         auto quot = lex_quotation_mark::invoke(inner_loc);
         if(!quot)
@@ -443,8 +456,10 @@ parse_basic_string(location<Container>& loc)
     }
     else
     {
-        loc.iter() = first; // rollback
+        loc.reset(first); // rollback
-        return err(token.unwrap_err());
+        return err(format_underline("[error] toml::parse_basic_string: "
+                   "the next token is not a string",
+                   {{std::addressof(loc), "here"}}));
     }
 }
 
@@ -482,8 +497,10 @@ parse_ml_literal_string(location<Container>& loc)
     }
     else
     {
-        loc.iter() = first; // rollback
+        loc.reset(first); // rollback
-        return err(token.unwrap_err());
+        return err(format_underline("[error] toml::parse_ml_literal_string: "
+                   "the next token is not a multiline literal string",
+                   {{std::addressof(loc), "here"}}));
     }
 }
 
@@ -519,8 +536,10 @@ parse_literal_string(location<Container>& loc)
     }
     else
     {
-        loc.iter() = first; // rollback
+        loc.reset(first); // rollback
-        return err(token.unwrap_err());
+        return err(format_underline("[error] toml::parse_literal_string: "
+                   "the next token is not a literal string",
+                   {{std::addressof(loc), "here"}}));
     }
 }
 
@@ -528,10 +547,30 @@ template<typename Container>
 result<std::pair<toml::string, region<Container>>, std::string>
 parse_string(location<Container>& loc)
 {
-    if(const auto rslt = parse_ml_basic_string(loc))   {return rslt;}
+    if(loc.iter() != loc.end() && *(loc.iter()) == '"')
-    if(const auto rslt = parse_ml_literal_string(loc)) {return rslt;}
+    {
-    if(const auto rslt = parse_basic_string(loc))      {return rslt;}
+        if(loc.iter() + 1 != loc.end() && *(loc.iter() + 1) == '"' &&
-    if(const auto rslt = parse_literal_string(loc))    {return rslt;}
+           loc.iter() + 2 != loc.end() && *(loc.iter() + 2) == '"')
+        {
+            return parse_ml_basic_string(loc);
+        }
+        else
+        {
+            return parse_basic_string(loc);
+        }
+    }
+    else if(loc.iter() != loc.end() && *(loc.iter()) == '\'')
+    {
+        if(loc.iter() + 1 != loc.end() && *(loc.iter() + 1) == '\'' &&
+           loc.iter() + 2 != loc.end() && *(loc.iter() + 2) == '\'')
+        {
+            return parse_ml_literal_string(loc);
+        }
+        else
+        {
+            return parse_literal_string(loc);
+        }
+    }
     return err(format_underline("[error] toml::parse_string: ",
                 {{std::addressof(loc), "the next token is not a string"}}));
 }
@@ -555,7 +594,7 @@ parse_local_date(location<Container>& loc)
                 "toml::parse_inner_local_date: invalid year format",
                 {{std::addressof(inner_loc), msg}}));
         }
-        ++inner_loc.iter();
+        inner_loc.advance();
         const auto m = lex_date_month::invoke(inner_loc);
         if(!m || inner_loc.iter() == inner_loc.end() || *inner_loc.iter() != '-')
         {
@@ -566,7 +605,7 @@ parse_local_date(location<Container>& loc)
                 "toml::parse_local_date: invalid month format",
                 {{std::addressof(inner_loc), msg}}));
         }
-        ++inner_loc.iter();
+        inner_loc.advance();
         const auto d = lex_date_mday::invoke(inner_loc);
         if(!d)
         {
@@ -583,7 +622,7 @@ parse_local_date(location<Container>& loc)
     }
     else
     {
-        loc.iter() = first;
+        loc.reset(first);
         return err(format_underline("[error]: toml::parse_local_date: ",
             {{std::addressof(loc), "the next token is not a local_date"}}));
     }
@@ -608,7 +647,7 @@ parse_local_time(location<Container>& loc)
                 "toml::parse_local_time: invalid year format",
                 {{std::addressof(inner_loc), msg}}));
         }
-        ++inner_loc.iter();
+        inner_loc.advance();
         const auto m = lex_time_minute::invoke(inner_loc);
         if(!m || inner_loc.iter() == inner_loc.end() || *inner_loc.iter() != ':')
         {
@@ -619,7 +658,7 @@ parse_local_time(location<Container>& loc)
                 "toml::parse_local_time: invalid month format",
                 {{std::addressof(inner_loc), msg}}));
         }
-        ++inner_loc.iter();
+        inner_loc.advance();
         const auto s = lex_time_second::invoke(inner_loc);
         if(!s)
         {
@@ -668,7 +707,7 @@ parse_local_time(location<Container>& loc)
     }
     else
     {
-        loc.iter() = first;
+        loc.reset(first);
         return err(format_underline("[error]: toml::parse_local_time: ",
             {{std::addressof(loc), "the next token is not a local_time"}}));
     }
@@ -692,13 +731,14 @@ parse_local_datetime(location<Container>& loc)
                 "toml::parse_local_datetime: invalid datetime format",
                 {{std::addressof(inner_loc), msg}}));
         }
-        const char delim = *(inner_loc.iter()++);
+        const char delim = *(inner_loc.iter());
         if(delim != 'T' && delim != 't' && delim != ' ')
         {
             throw internal_error(format_underline("[error]: "
                 "toml::parse_local_datetime: invalid datetime format",
                 {{std::addressof(inner_loc), "should be `T` or ` ` (space)"}}));
         }
+        inner_loc.advance();
         const auto time = parse_local_time(inner_loc);
         if(!time)
         {
@@ -712,7 +752,7 @@ parse_local_datetime(location<Container>& loc)
     }
     else
     {
-        loc.iter() = first;
+        loc.reset(first);
         return err(format_underline("[error]: toml::parse_local_datetime: ",
             {{std::addressof(loc), "the next token is not a local_datetime"}}));
     }
@@ -762,9 +802,9 @@ parse_offset_datetime(location<Container>& loc)
     }
     else
     {
-        loc.iter() = first;
+        loc.reset(first);
         return err(format_underline("[error]: toml::parse_offset_datetime: ",
-            {{std::addressof(loc), "the next token is not a local_datetime"}}));
+            {{std::addressof(loc), "the next token is not a offset_datetime"}}));
     }
 }
 
@@ -823,7 +863,7 @@ parse_key(location<Container>& loc)
             }
             else if(*inner_loc.iter() == '.')
             {
-                ++inner_loc.iter(); // to skip `.`
+                inner_loc.advance(); // to skip `.`
             }
             else
             {
@@ -834,7 +874,7 @@ parse_key(location<Container>& loc)
         }
         return ok(std::make_pair(keys, reg));
     }
-    loc.iter() = first;
+    loc.reset(first);
 
     // simple key -> foo
     if(const auto smpl = parse_simple_key(loc))
@@ -863,7 +903,7 @@ parse_array(location<Container>& loc)
     {
         return err("[error] toml::parse_array: token is not an array");
     }
-    ++loc.iter();
+    loc.advance();
 
     using lex_ws_comment_newline = repeat<
         either<lex_wschar, lex_newline, lex_comment>, unlimited>;
@@ -875,7 +915,7 @@ parse_array(location<Container>& loc)
 
         if(loc.iter() != loc.end() && *loc.iter() == ']')
         {
-            ++loc.iter(); // skip ']'
+            loc.advance(); // skip ']'
             return ok(std::make_pair(retval,
                       region<Container>(loc, first, loc.iter())));
         }
@@ -885,7 +925,7 @@ parse_array(location<Container>& loc)
             if(!retval.empty() && retval.front().type() != val.as_ok().type())
             {
                 auto array_start_loc = loc;
-                array_start_loc.iter() = first;
+                array_start_loc.reset(first);
 
                 throw syntax_error(format_underline("[error] toml::parse_array: "
                     "type of elements should be the same each other.", {
@@ -905,7 +945,7 @@ parse_array(location<Container>& loc)
         else
         {
             auto array_start_loc = loc;
-            array_start_loc.iter() = first;
+            array_start_loc.reset(first);
 
             throw syntax_error(format_underline("[error] toml::parse_array: "
                 "value having invalid format appeared in an array", {
@@ -921,14 +961,14 @@ parse_array(location<Container>& loc)
             lex_ws_comment_newline::invoke(loc);
             if(loc.iter() != loc.end() && *loc.iter() == ']')
             {
-                ++loc.iter(); // skip ']'
+                loc.advance(); // skip ']'
                 return ok(std::make_pair(retval,
                           region<Container>(loc, first, loc.iter())));
             }
             else
             {
                 auto array_start_loc = loc;
-                array_start_loc.iter() = first;
+                array_start_loc.reset(first);
 
                 throw syntax_error(format_underline("[error] toml::parse_array:"
                     " missing array separator `,` after a value", {
@@ -938,7 +978,7 @@ parse_array(location<Container>& loc)
             }
         }
     }
-    loc.iter() = first;
+    loc.reset(first);
     throw syntax_error(format_underline("[error] toml::parse_array: "
             "array did not closed by `]`",
             {{std::addressof(loc), "should be closed"}}));
@@ -957,7 +997,7 @@ parse_key_value_pair(location<Container>& loc)
         // key. then we need to show error as "empty key is not allowed".
         if(const auto keyval_sep = lex_keyval_sep::invoke(loc))
         {
-            loc.iter() = first;
+            loc.reset(first);
             msg = format_underline("[error] toml::parse_key_value_pair: "
                 "empty key is not allowed.",
                 {{std::addressof(loc), "key expected before '='"}});
@@ -986,7 +1026,7 @@ parse_key_value_pair(location<Container>& loc)
                 "missing key-value separator `=`",
                 {{std::addressof(loc), "should be `=`"}});
         }
-        loc.iter() = first;
+        loc.reset(first);
         return err(std::move(msg));
     }
 
@@ -995,11 +1035,11 @@ parse_key_value_pair(location<Container>& loc)
     if(!val)
     {
         std::string msg;
-        loc.iter() = after_kvsp;
+        loc.reset(after_kvsp);
         // check there is something not a comment/whitespace after `=`
         if(sequence<maybe<lex_ws>, maybe<lex_comment>, lex_newline>::invoke(loc))
         {
-            loc.iter() = after_kvsp;
+            loc.reset(after_kvsp);
             msg = format_underline("[error] toml::parse_key_value_pair: "
                     "missing value after key-value separator '='",
                     {{std::addressof(loc), "expected value, but got nothing"}});
@@ -1008,7 +1048,7 @@ parse_key_value_pair(location<Container>& loc)
         {
             msg = std::move(val.unwrap_err());
         }
-        loc.iter() = first;
+        loc.reset(first);
         return err(msg);
     }
     return ok(std::make_pair(std::move(key_reg.unwrap()),
@@ -1035,6 +1075,7 @@ std::string format_dotted_keys(InputIterator first, const InputIterator last)
 template<typename Container>
 result<std::pair<std::vector<key>, region<Container>>, std::string>
 parse_table_key(location<Container>& loc);
+
 // The following toml file is allowed.
 // ```toml
 // [a.b.c]     # here, table `a` has element `b`.
@@ -1325,14 +1366,14 @@ parse_inline_table(location<Container>& loc)
         return err(format_underline("[error] toml::parse_inline_table: ", 
             {{std::addressof(loc), "the next token is not an inline table"}}));
     }
-    ++loc.iter();
+    loc.advance();
     // it starts from "{". it should be formatted as inline-table
     while(loc.iter() != loc.end())
     {
         maybe<lex_ws>::invoke(loc);
         if(loc.iter() != loc.end() && *loc.iter() == '}')
         {
-            ++loc.iter(); // skip `}`
+            loc.advance(); // skip `}`
             return ok(std::make_pair(
                         retval, region<Container>(loc, first, loc.iter())));
         }
@@ -1361,24 +1402,70 @@ parse_inline_table(location<Container>& loc)
             maybe<lex_ws>::invoke(loc);
             if(loc.iter() != loc.end() && *loc.iter() == '}')
             {
-                ++loc.iter(); // skip `}`
+                loc.advance(); // skip `}`
                 return ok(std::make_pair(
                             retval, region<Container>(loc, first, loc.iter())));
             }
+            else if(*loc.iter() == '#' || *loc.iter() == '\r' || *loc.iter() == '\n')
+            {
+                throw syntax_error(format_underline("[error] "
+                    "toml::parse_inline_table: missing curly brace `}`",
+                    {{std::addressof(loc), "should be `}`"}}));
+            }
             else
             {
                 throw syntax_error(format_underline("[error] "
-                    "toml:::parse_inline_table: missing table separator `,` ",
+                    "toml::parse_inline_table: missing table separator `,` ",
                     {{std::addressof(loc), "should be `,`"}}));
             }
         }
     }
-    loc.iter() = first;
+    loc.reset(first);
     throw syntax_error(format_underline("[error] toml::parse_inline_table: "
             "inline table did not closed by `}`",
             {{std::addressof(loc), "should be closed"}}));
 }
 
+template<typename Container>
+value_t guess_number_type(const location<Container>& l)
+{
+    location<Container> loc = l;
+
+    if(lex_offset_date_time::invoke(loc)) {return value_t::OffsetDatetime;}
+    loc.reset(l.iter());
+
+    if(lex_local_date_time::invoke(loc)) {return value_t::LocalDatetime;}
+    loc.reset(l.iter());
+
+    if(lex_local_date::invoke(loc)) {return value_t::LocalDate;}
+    loc.reset(l.iter());
+
+    if(lex_local_time::invoke(loc)) {return value_t::LocalTime;}
+    loc.reset(l.iter());
+
+    if(lex_float::invoke(loc)) {return value_t::Float;}
+    loc.reset(l.iter());
+
+    return value_t::Integer;
+}
+
+template<typename Container>
+value_t guess_value_type(const location<Container>& loc)
+{
+    switch(*loc.iter())
+    {
+        case '"' : {return value_t::String; }
+        case '\'': {return value_t::String; }
+        case 't' : {return value_t::Boolean;}
+        case 'f' : {return value_t::Boolean;}
+        case '[' : {return value_t::Array;  }
+        case '{' : {return value_t::Table;  }
+        case 'i' : {return value_t::Float;  } // inf.
+        case 'n' : {return value_t::Float;  } // nan.
+        default  : {return guess_number_type(loc);}
+    }
+}
+
 template<typename Container>
 result<value, std::string> parse_value(location<Container>& loc)
 {
@@ -1388,32 +1475,28 @@ result<value, std::string> parse_value(location<Container>& loc)
         return err(format_underline("[error] toml::parse_value: input is empty",
                    {{std::addressof(loc), ""}}));
     }
-    if(auto r = parse_string         (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_array          (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_inline_table   (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_boolean        (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_offset_datetime(loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_local_datetime (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_local_date     (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_local_time     (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_floating       (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
-    if(auto r = parse_integer        (loc))
-    {return ok(value(std::move(r.unwrap().first), std::move(r.unwrap().second)));}
 
+    switch(guess_value_type(loc))
+    {
+        case value_t::Boolean        : {return parse_boolean(loc);        }
+        case value_t::Integer        : {return parse_integer(loc);        }
+        case value_t::Float          : {return parse_floating(loc);       }
+        case value_t::String         : {return parse_string(loc);         }
+        case value_t::OffsetDatetime : {return parse_offset_datetime(loc);}
+        case value_t::LocalDatetime  : {return parse_local_datetime(loc); }
+        case value_t::LocalDate      : {return parse_local_date(loc);     }
+        case value_t::LocalTime      : {return parse_local_time(loc);     }
+        case value_t::Array          : {return parse_array(loc);          }
+        case value_t::Table          : {return parse_inline_table(loc);   }
+        default:
+        {
             const auto msg = format_underline("[error] toml::parse_value: "
                     "unknown token appeared", {{std::addressof(loc), "unknown"}});
-    loc.iter() = first;
+            loc.reset(first);
             return err(msg);
         }
+    }
+}
 
 template<typename Container>
 result<std::pair<std::vector<key>, region<Container>>, std::string>
@@ -1468,7 +1551,8 @@ parse_table_key(location<Container>& loc)
     }
     else
     {
-        return err(token.unwrap_err());
+        return err(format_underline("[error] toml::parse_table_key: "
+            "not a valid table key", {{std::addressof(loc), "here"}}));
     }
 }
 
@@ -1476,7 +1560,7 @@ template<typename Container>
 result<std::pair<std::vector<key>, region<Container>>, std::string>
 parse_array_table_key(location<Container>& loc)
 {
-    if(auto token = lex_array_table::invoke(loc))
+    if(auto token = lex_array_table::invoke(loc, true))
     {
         location<std::string> inner_loc(loc.name(), token.unwrap().str());
 
@@ -1521,7 +1605,8 @@ parse_array_table_key(location<Container>& loc)
     }
     else
     {
-        return err(token.unwrap_err());
+        return err(format_underline("[error] toml::parse_array_table_key: "
+            "not a valid table key", {{std::addressof(loc), "here"}}));
     }
 }
 
@@ -1547,12 +1632,12 @@ result<table, std::string> parse_ml_table(location<Container>& loc)
         const auto before = loc.iter();
         if(const auto tmp = parse_array_table_key(loc)) // next table found
         {
-            loc.iter() = before;
+            loc.reset(before);
             return ok(tab);
         }
         if(const auto tmp = parse_table_key(loc)) // next table found
         {
-            loc.iter() = before;
+            loc.reset(before);
             return ok(tab);
         }
 
@@ -1592,7 +1677,7 @@ result<table, std::string> parse_ml_table(location<Container>& loc)
             const auto msg = format_underline("[error] toml::parse_table: "
                 "invalid line format", {{std::addressof(loc), concat_to_string(
                 "expected newline, but got '", show_char(*loc.iter()), "'.")}});
-            loc.iter() = before;
+            loc.reset(before);
             return err(msg);
         }
 
@@ -1695,7 +1780,7 @@ inline table parse(std::istream& is, std::string fname = "unknown file")
         std::memcpy(BOM.data(), loc.source()->data(), 3);
         if(BOM[0] == 0xEF && BOM[1] == 0xBB && BOM[2] == 0xBF)
         {
-            loc.iter() += 3; // BOM found. skip.
+            loc.advance(3); // BOM found. skip.
         }
     }
 

toml/region.hpp

@@ -1,7 +1,7 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_REGION_H
+#ifndef TOML11_REGION_HPP
-#define TOML11_REGION_H
+#define TOML11_REGION_HPP
 #include "exception.hpp"
 #include <memory>
 #include <vector>
@@ -15,7 +15,7 @@ namespace toml
 namespace detail
 {
 
-// helper function to avoid std::string(0, 'c')
+// helper function to avoid std::string(0, 'c') or std::string(iter, iter)
 template<typename Iterator>
 std::string make_string(Iterator first, Iterator last)
 {
@@ -28,9 +28,7 @@ inline std::string make_string(std::size_t len, char c)
     return std::string(len, c);
 }
 
-// region in a container, normally in a file content.
+// region_base is a base class of location and region that are defined below.
-// shared_ptr points the resource that the iter points.
-// combinators returns this.
 // it will be used to generate better error messages.
 struct region_base
 {
@@ -48,25 +46,40 @@ struct region_base
     virtual std::string line()     const {return std::string("unknown line");}
     virtual std::string line_num() const {return std::string("?");}
 
-    virtual std::size_t before()   const noexcept {return 0;}
+    // length of the region
     virtual std::size_t size()     const noexcept {return 0;}
+    // number of characters in the line before the region
+    virtual std::size_t before()   const noexcept {return 0;}
+    // number of characters in the line after the region
     virtual std::size_t after()    const noexcept {return 0;}
+
+    virtual std::string comment_before() const {return "";} // just before
+    virtual std::string comment_inline() const {return "";} // in the same line
+    virtual std::string comment()        const {return "";} // concatenate
+    // ```toml
+    // # comment_before
+    // key = "value" # comment_inline
+    // ```
 };
 
-// location in a container, normally in a file content.
+// location represents a position in a container, which contains a file content.
-// shared_ptr points the resource that the iter points.
-// it can be used not only for resource handling, but also error message.
-//
 // it can be considered as a region that contains only one character.
+//
+// it contains pointer to the file content and iterator that points the current
+// location.
 template<typename Container>
 struct location final : public region_base
 {
-    static_assert(std::is_same<char, typename Container::value_type>::value,"");
     using const_iterator = typename Container::const_iterator;
     using source_ptr     = std::shared_ptr<const Container>;
 
+    static_assert(std::is_same<char, typename Container::value_type>::value,"");
+    static_assert(std::is_same<std::random_access_iterator_tag,
+        typename std::iterator_traits<const_iterator>::iterator_category>::value,
+        "container should be randomly accessible");
+
     location(std::string name, Container cont)
-      : source_(std::make_shared<Container>(std::move(cont))),
+      : source_(std::make_shared<Container>(std::move(cont))), line_number_(1),
         source_name_(std::move(name)), iter_(source_->cbegin())
     {}
     location(const location&) = default;
@@ -77,18 +90,54 @@ struct location final : public region_base
 
     bool is_ok() const noexcept override {return static_cast<bool>(source_);}
 
-    const_iterator& iter()       noexcept {return iter_;}
+    // this const prohibits codes like `++(loc.iter())`.
-    const_iterator  iter() const noexcept {return iter_;}
+    const const_iterator iter()  const noexcept {return iter_;}
 
     const_iterator begin() const noexcept {return source_->cbegin();}
     const_iterator end()   const noexcept {return source_->cend();}
 
+    // XXX `location::line_num()` used to be implemented using `std::count` to
+    // count a number of '\n'. But with a long toml file (typically, 10k lines),
+    // it becomes intolerably slow because each time it generates error messages,
+    // it counts '\n' from thousands of characters. To workaround it, I decided
+    // to introduce `location::line_number_` member variable and synchronize it
+    // to the location changes the point to look. So an overload of `iter()`
+    // which returns mutable reference is removed and `advance()`, `retrace()`
+    // and `reset()` is added.
+    void advance(std::size_t n = 1) noexcept
+    {
+        this->line_number_ += std::count(this->iter_, this->iter_ + n, '\n');
+        this->iter_ += n;
+        return;
+    }
+    void retrace(std::size_t n = 1) noexcept
+    {
+        this->line_number_ -= std::count(this->iter_ - n, this->iter_, '\n');
+        this->iter_ -= n;
+        return;
+    }
+    void reset(const_iterator rollback) noexcept
+    {
+        // since c++11, std::distance works in both ways for random-access
+        // iterators and returns a negative value if `first > last`.
+        if(0 <= std::distance(rollback, this->iter_)) // rollback < iter
+        {
+            this->line_number_ -= std::count(rollback, this->iter_, '\n');
+        }
+        else // iter < rollback [[unlikely]]
+        {
+            this->line_number_ += std::count(this->iter_, rollback, '\n');
+        }
+        this->iter_ = rollback;
+        return;
+    }
+
     std::string str()  const override {return make_string(1, *this->iter());}
     std::string name() const override {return source_name_;}
 
     std::string line_num() const override
     {
-        return std::to_string(1+std::count(this->begin(), this->iter(), '\n'));
+        return std::to_string(this->line_number_);
     }
 
     std::string line() const override
@@ -127,17 +176,26 @@ struct location final : public region_base
   private:
 
     source_ptr     source_;
+    std::size_t    line_number_;
     std::string    source_name_;
     const_iterator iter_;
 };
 
+// region represents a range in a container, which contains a file content.
+//
+// it contains pointer to the file content and iterator that points the first
+// and last location.
 template<typename Container>
 struct region final : public region_base
 {
-    static_assert(std::is_same<char, typename Container::value_type>::value,"");
     using const_iterator = typename Container::const_iterator;
     using source_ptr     = std::shared_ptr<const Container>;
 
+    static_assert(std::is_same<char, typename Container::value_type>::value,"");
+    static_assert(std::is_same<std::random_access_iterator_tag,
+        typename std::iterator_traits<const_iterator>::iterator_category>::value,
+        "container should be randomly accessible");
+
     // delete default constructor. source_ never be null.
     region() = delete;
 
@@ -230,6 +288,92 @@ struct region final : public region_base
 
     std::string name() const override {return source_name_;}
 
+    std::string comment_before() const override
+    {
+        auto iter = this->line_begin(); // points the first element
+        std::vector<std::pair<decltype(iter), decltype(iter)>> comments;
+        while(iter != this->begin())
+        {
+            iter = std::prev(iter);
+            using rev_iter = std::reverse_iterator<decltype(iter)>;
+            auto line_before = std::find(rev_iter(iter), rev_iter(this->begin()),
+                                         '\n').base();
+            // range [line_before, iter) represents the previous line
+
+            auto comment_found = std::find(line_before, iter, '#');
+            if(iter != comment_found && std::all_of(line_before, comment_found,
+                    [](const char c) noexcept -> bool {
+                        return c == ' ' || c == '\t';
+                    }))
+            {
+                // the line before this range contains only a comment.
+                comments.push_back(std::make_pair(comment_found, iter));
+            }
+            else
+            {
+                break;
+            }
+            iter = line_before;
+        }
+
+        std::string com;
+        for(auto i = comments.crbegin(), e = comments.crend(); i!=e; ++i)
+        {
+            if(i != comments.crbegin()) {com += '\n';}
+            com += std::string(i->first, i->second);
+        }
+        return com;
+    }
+
+    std::string comment_inline() const override
+    {
+        if(this->contain_newline())
+        {
+            std::string com;
+            // check both the first and the last line.
+            const auto first_line_end =
+                std::find(this->line_begin(), this->last(), '\n');
+            const auto first_comment_found =
+                std::find(this->line_begin(), first_line_end, '#');
+
+            if(first_comment_found != first_line_end)
+            {
+                com += std::string(first_comment_found, first_line_end);
+            }
+
+            const auto last_comment_found =
+                std::find(this->last(), this->line_end(), '#');
+            if(last_comment_found != this->line_end())
+            {
+                if(!com.empty()){com += '\n';}
+                com += std::string(last_comment_found, this->line_end());
+            }
+            return com;
+        }
+        const auto comment_found =
+            std::find(this->line_begin(), this->line_end(), '#');
+        return std::string(comment_found, this->line_end());
+    }
+
+    std::string comment() const override
+    {
+        std::string com_bef = this->comment_before();
+        std::string com_inl = this->comment_inline();
+        if(!com_bef.empty() && !com_inl.empty())
+        {
+            com_bef += '\n';
+            return com_bef + com_inl;
+        }
+        else if(com_bef.empty())
+        {
+            return com_inl;
+        }
+        else
+        {
+            return com_bef;
+        }
+    }
+
   private:
 
     source_ptr     source_;
@@ -293,7 +437,8 @@ inline std::string format_underline(const std::string& message,
         {
             // invalid
             // ~~~~~~~
-            retval << make_string(reg->size(), '~');
+            const auto underline_len = std::min(reg->size(), reg->line().size());
+            retval << make_string(underline_len, '~');
         }
 
         retval << ' ';

toml/result.hpp

@@ -1,7 +1,7 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_RESULT_H
+#ifndef TOML11_RESULT_HPP
-#define TOML11_RESULT_H
+#define TOML11_RESULT_HPP
 #include "traits.hpp"
 #include <type_traits>
 #include <stdexcept>

toml/serializer.hpp

@@ -36,7 +36,7 @@ struct serializer
         std::vector<char> buf(bsz + 1, '\0'); // +1 for null character(\0)
         std::snprintf(buf.data(), buf.size(), fmt, this->float_prec_, f);
 
-        std::string token(buf.begin(), buf.end());
+        std::string token(buf.begin(), std::prev(buf.end()));
         if(token.back() == '.') // 1. => 1.0
         {
             token += '0';
@@ -483,15 +483,19 @@ struct serializer
 
 inline std::string
 format(const value& v, std::size_t w = 80,
-       int fprec = std::numeric_limits<toml::floating>::max_digits10)
+       int fprec = std::numeric_limits<toml::floating>::max_digits10,
+       bool force_inline = false)
 {
-    return visit(serializer(w, fprec, true), v);
+    // if value is a table, it is considered to be a root object.
+    // the root object can't be an inline table. so pass false. otherwise, true.
+    return visit(serializer(w, fprec, (!v.is_table()) || force_inline), v);
 }
 inline std::string
 format(const table& t, std::size_t w = 80,
-       int fprec = std::numeric_limits<toml::floating>::max_digits10)
+       int fprec = std::numeric_limits<toml::floating>::max_digits10,
+       bool force_inline = false)
 {
-    return serializer(w, fprec, true)(t);
+    return serializer(w, fprec, force_inline)(t);
 }
 
 template<typename charT, typename traits>
@@ -506,6 +510,18 @@ operator<<(std::basic_ostream<charT, traits>& os, const value& v)
     os << visit(serializer(w, fprec, false), v);
     return os;
 }
+template<typename charT, typename traits>
+std::basic_ostream<charT, traits>&
+operator<<(std::basic_ostream<charT, traits>& os, const table& v)
+{
+    // get status of std::setw().
+    const std::size_t w     = os.width();
+    const int         fprec = os.precision();
+    os.width(0);
+    // the root object can't be an inline table. so pass `false`.
+    os << serializer(w, fprec, false)(v);
+    return os;
+}
 
 } // toml
 #endif// TOML11_SERIALIZER_HPP

toml/string.hpp

@@ -1,9 +1,14 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_STRING_H
+#ifndef TOML11_STRING_HPP
-#define TOML11_STRING_H
+#define TOML11_STRING_HPP
 #include <string>
 #include <cstdint>
+#if __cplusplus >= 201703L
+#if __has_include(<string_view>)
+#include <string_view>
+#endif
+#endif
 
 namespace toml
 {
@@ -40,6 +45,17 @@ struct string
     operator std::string const& () const& noexcept {return str;}
     operator std::string&&      () &&     noexcept {return std::move(str);}
 
+#if __cplusplus >= 201703L
+    explicit string(std::string_view s): kind(string_t::basic), str(s){}
+    string(std::string_view s, string_t k): kind(k), str(s){}
+
+    string& operator=(std::string_view s)
+    {kind = string_t::basic; str = s; return *this;}
+
+    explicit operator std::string_view() const noexcept
+    {return std::string_view(str);}
+#endif
+
     string_t    kind;
     std::string str;
 };

toml/to_toml.hpp

@@ -1,49 +0,0 @@
-//     Copyright Toru Niina 2017.
-// Distributed under the MIT License.
-#ifndef TOML11_TO_TOML
-#define TOML11_TO_TOML
-#include "value.hpp"
-
-namespace toml
-{
-
-template<typename T>
-TOML11_MARK_AS_DEPRECATED
-inline value to_toml(T&& x)
-{
-    return value(std::forward<T>(x));
-}
-
-template<typename T>
-TOML11_MARK_AS_DEPRECATED
-inline value to_toml(T&& x, string_t kind)
-{
-    return value(std::forward<T>(x), kind);
-}
-
-TOML11_MARK_AS_DEPRECATED
-inline value to_toml(local_date d, local_time t)
-{
-    return value(local_datetime(d, t));
-}
-TOML11_MARK_AS_DEPRECATED
-inline value to_toml(local_date d, local_time t, time_offset ofs)
-{
-    return value(offset_datetime(d, t, ofs));
-}
-
-template<typename ... Ts>
-TOML11_MARK_AS_DEPRECATED
-inline value to_toml(Ts&& ... xs)
-{
-    return value(toml::array{toml::value(std::forward<Ts>(xs)) ... });
-}
-
-TOML11_MARK_AS_DEPRECATED
-inline value to_toml(std::initializer_list<std::pair<std::string, toml::value>> xs)
-{
-    return value(toml::table(xs.begin(), xs.end()));
-}
-
-} // toml
-#endif // TOML11_TO_TOML

toml/traits.hpp

@@ -1,7 +1,7 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_TRAITS
+#ifndef TOML11_TRAITS_HPP
-#define TOML11_TRAITS
+#define TOML11_TRAITS_HPP
 #include <type_traits>
 #include <utility>
 #include <chrono>
@@ -9,6 +9,9 @@
 
 namespace toml
 {
+
+class value; // forward decl
+
 namespace detail
 {
 
@@ -45,6 +48,22 @@ struct has_resize_method_impl
     template<typename T> static std::false_type check(...);
 };
 
+struct has_from_toml_method_impl
+{
+    template<typename T>
+    static std::true_type  check(
+        decltype(std::declval<T>().from_toml(std::declval<::toml::value>()))*);
+    template<typename T>
+    static std::false_type check(...);
+};
+struct has_into_toml_method_impl
+{
+    template<typename T>
+    static std::true_type  check(decltype(std::declval<T>().into_toml())*);
+    template<typename T>
+    static std::false_type check(...);
+};
+
 /// Intel C++ compiler can not use decltype in parent class declaration, here
 /// is a hack to work around it. https://stackoverflow.com/a/23953090/4692076
 #ifdef __INTEL_COMPILER
@@ -62,6 +81,14 @@ struct has_mapped_type : decltype(has_mapped_type_impl::check<T>(nullptr)){};
 template<typename T>
 struct has_resize_method : decltype(has_resize_method_impl::check<T>(nullptr)){};
 
+
+template<typename T>
+struct has_from_toml_method
+: decltype(has_from_toml_method_impl::check<T>(nullptr)){};
+template<typename T>
+struct has_into_toml_method
+: decltype(has_into_toml_method_impl::check<T>(nullptr)){};
+
 #ifdef __INTEL_COMPILER
 #undef decltype(...)
 #endif
@@ -142,6 +169,21 @@ using return_type_of_t = typename std::result_of<F(Args...)>::type;
 
 #endif
 
+// ---------------------------------------------------------------------------
+// is_string_literal
+//
+// to use this, pass `typename remove_reference<T>::type` to T.
+
+template<typename T>
+struct is_string_literal:
+disjunction<
+    std::is_same<const char*, T>,
+    conjunction<
+        std::is_array<T>,
+        std::is_same<const char, typename std::remove_extent<T>::type>
+        >
+    >{};
+
 }// detail
 }//toml
 #endif // TOML_TRAITS

toml/types.hpp

@@ -1,12 +1,17 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_TYPES_H
+#ifndef TOML11_TYPES_HPP
-#define TOML11_TYPES_H
+#define TOML11_TYPES_HPP
 #include "datetime.hpp"
 #include "string.hpp"
 #include "traits.hpp"
 #include <vector>
 #include <unordered_map>
+#if __cplusplus >= 201703L
+#if __has_include(<string_view>)
+#include <string_view>
+#endif
+#endif
 
 namespace toml
 {
@@ -172,6 +177,9 @@ template<typename T>
 struct is_container : conjunction<
     negation<is_map<T>>,
     negation<std::is_same<T, std::string>>,
+#if __cplusplus >= 201703L
+    negation<std::is_same<T, std::string_view>>,
+#endif
     has_iterator<T>,
     has_value_type<T>
     >{};

toml/utility.hpp

@@ -1,18 +1,18 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_UTILITY
+#ifndef TOML11_UTILITY_HPP
-#define TOML11_UTILITY
+#define TOML11_UTILITY_HPP
 #include "traits.hpp"
 #include <utility>
 #include <memory>
 #include <sstream>
 
 #if __cplusplus >= 201402L
-#  define TOML11_MARK_AS_DEPRECATED [[deprecated]]
+#  define TOML11_MARK_AS_DEPRECATED(msg) [[deprecated(msg)]]
 #elif defined(__GNUC__)
-#  define TOML11_MARK_AS_DEPRECATED __attribute__((deprecated))
+#  define TOML11_MARK_AS_DEPRECATED(msg) __attribute__((deprecated(msg)))
 #elif defined(_MSC_VER)
-#  define TOML11_MARK_AS_DEPRECATED __declspec(deprecated)
+#  define TOML11_MARK_AS_DEPRECATED(msg) __declspec(deprecated(msg))
 #else
 #  define TOML11_MARK_AS_DEPRECATED
 #endif

toml/value.hpp

@@ -1,8 +1,9 @@
 //     Copyright Toru Niina 2017.
 // Distributed under the MIT License.
-#ifndef TOML11_VALUE
+#ifndef TOML11_VALUE_HPP
-#define TOML11_VALUE
+#define TOML11_VALUE_HPP
 #include "traits.hpp"
+#include "into.hpp"
 #include "utility.hpp"
 #include "exception.hpp"
 #include "storage.hpp"
@@ -13,6 +14,9 @@
 #include <unordered_map>
 #include <cassert>
 #include <cstdint>
+#if __cplusplus >= 201703L
+#include <string_view>
+#endif
 
 namespace toml
 {
@@ -292,6 +296,29 @@ class value
         assigner(this->string_, toml::string(std::string(s), kind));
     }
 
+#if __cplusplus >= 201703L
+    value(std::string_view s)
+        : type_(value_t::String),
+          region_info_(std::make_shared<region_base>(region_base{}))
+    {
+        assigner(this->string_, toml::string(s));
+    }
+    value& operator=(std::string_view s)
+    {
+        this->cleanup();
+        this->type_ = value_t::String;
+        this->region_info_ = std::make_shared<region_base>(region_base{});
+        assigner(this->string_, toml::string(s));
+        return *this;
+    }
+    value(std::string_view s, string_t kind)
+        : type_(value_t::String),
+          region_info_(std::make_shared<region_base>(region_base{}))
+    {
+        assigner(this->string_, toml::string(s, kind));
+    }
+#endif
+
     // local date ===========================================================
 
     value(const local_date& ld)
@@ -473,7 +500,7 @@ class value
           region_info_(std::make_shared<region_base>(region_base{}))
     {
         array ary; ary.reserve(list.size());
-        for(auto& elem : list) {ary.emplace_back(std::move(elem));}
+        for(const auto& elem : list) {ary.emplace_back(elem);}
         assigner(this->array_, std::move(ary));
     }
     template<typename T, typename std::enable_if<detail::is_container<T>::value,
@@ -485,7 +512,7 @@ class value
         this->region_info_ = std::make_shared<region_base>(region_base{});
 
         array ary; ary.reserve(list.size());
-        for(auto& elem : list) {ary.emplace_back(std::move(elem));}
+        for(const auto& elem : list) {ary.emplace_back(elem);}
         assigner(this->array_, std::move(ary));
         return *this;
     }
@@ -533,10 +560,70 @@ class value
         return *this;
     }
 
+    // user-defined =========================================================
+
+    // convert using into_toml() method -------------------------------------
+
+    template<typename T, typename std::enable_if<detail::conjunction<
+        detail::negation<detail::is_exact_toml_type<T>>, // not a toml::value
+        detail::has_into_toml_method<T> // but has `into_toml` method
+        >::value, std::nullptr_t>::type = nullptr>
+    value(const T& ud): value(ud.into_toml()) {}
+
+    template<typename T, typename std::enable_if<detail::conjunction<
+        detail::negation<detail::is_exact_toml_type<T>>, // not a toml::value
+        detail::has_into_toml_method<T> // but has `into_toml` method
+        >::value, std::nullptr_t>::type = nullptr>
+    value& operator=(const T& ud)
+    {
+        *this = ud.into_toml();
+        return *this;
+    }
+
+    // convert using into<T> struct -----------------------------------------
+
+    template<typename T, typename std::enable_if<
+        detail::negation<detail::is_exact_toml_type<T>>::value,
+        std::nullptr_t>::type = nullptr,
+        std::size_t S = sizeof(::toml::into<T>)>
+    value(const T& ud): value(::toml::into<T>::into_toml(ud)) {}
+
+    template<typename T, typename std::enable_if<
+        detail::negation<detail::is_exact_toml_type<T>>::value,
+        std::nullptr_t>::type = nullptr,
+        std::size_t S = sizeof(::toml::into<T>)>
+    value& operator=(const T& ud)
+    {
+        *this = ::toml::into<T>::into_toml(ud);
+        return *this;
+    }
+
+    // for internal use ------------------------------------------------------
+
+    template<typename T, typename Container, typename std::enable_if<
+        detail::is_exact_toml_type<T>::value, std::nullptr_t>::type = nullptr>
+    value(std::pair<T, detail::region<Container>> parse_result)
+        : value(std::move(parse_result.first), std::move(parse_result.second))
+    {}
+
+    // type checking and casting ============================================
+
     template<typename T>
     bool is() const noexcept {return value_traits<T>::type_index == this->type_;}
     bool is(value_t t) const noexcept {return t == this->type_;}
 
+    bool is_uninitialized()   const noexcept {return this->is(value_t::Empty         );}
+    bool is_boolean()         const noexcept {return this->is(value_t::Boolean       );}
+    bool is_integer()         const noexcept {return this->is(value_t::Integer       );}
+    bool is_float()           const noexcept {return this->is(value_t::Float         );}
+    bool is_string()          const noexcept {return this->is(value_t::String        );}
+    bool is_offset_datetime() const noexcept {return this->is(value_t::OffsetDatetime);}
+    bool is_local_datetime()  const noexcept {return this->is(value_t::LocalDatetime );}
+    bool is_local_date()      const noexcept {return this->is(value_t::LocalDate     );}
+    bool is_local_time()      const noexcept {return this->is(value_t::LocalTime     );}
+    bool is_array()           const noexcept {return this->is(value_t::Array         );}
+    bool is_table()           const noexcept {return this->is(value_t::Table         );}
+
     value_t type() const {return type_;}
 
     template<value_t T>
@@ -546,6 +633,41 @@ class value
     template<value_t T>
     typename detail::toml_default_type<T>::type&&      cast() &&;
 
+    boolean         const& as_boolean()         const {return this->cast<value_t::Boolean       >();}
+    integer         const& as_integer()         const {return this->cast<value_t::Integer       >();}
+    floating        const& as_float()           const {return this->cast<value_t::Float         >();}
+    string          const& as_string()          const {return this->cast<value_t::String        >();}
+    offset_datetime const& as_offset_datetime() const {return this->cast<value_t::OffsetDatetime>();}
+    local_datetime  const& as_local_datetime()  const {return this->cast<value_t::LocalDatetime >();}
+    local_date      const& as_local_date()      const {return this->cast<value_t::LocalDate     >();}
+    local_time      const& as_local_time()      const {return this->cast<value_t::LocalTime     >();}
+    array           const& as_array()           const {return this->cast<value_t::Array         >();}
+    table           const& as_table()           const {return this->cast<value_t::Table         >();}
+
+    boolean&          as_boolean()         {return this->cast<value_t::Boolean       >();}
+    integer&          as_integer()         {return this->cast<value_t::Integer       >();}
+    floating&         as_float()           {return this->cast<value_t::Float         >();}
+    string&           as_string()          {return this->cast<value_t::String        >();}
+    offset_datetime&  as_offset_datetime() {return this->cast<value_t::OffsetDatetime>();}
+    local_datetime&   as_local_datetime()  {return this->cast<value_t::LocalDatetime >();}
+    local_date&       as_local_date()      {return this->cast<value_t::LocalDate     >();}
+    local_time&       as_local_time()      {return this->cast<value_t::LocalTime     >();}
+    array&            as_array()           {return this->cast<value_t::Array         >();}
+    table&            as_table()           {return this->cast<value_t::Table         >();}
+
+    std::string comment() const
+    {
+        return this->region_info_->comment();
+    }
+    std::string comment_before() const
+    {
+        return this->region_info_->comment_before();
+    }
+    std::string comment_inline() const
+    {
+        return this->region_info_->comment_inline();
+    }
+
   private:
 
     void cleanup() noexcept
@@ -794,38 +916,40 @@ inline bool operator>=(const toml::value& lhs, const toml::value& rhs)
     return !(lhs < rhs);
 }
 
-namespace detail
+inline std::string format_error(const std::string& err_msg,
-{
-inline std::string format_error_impl(const std::string& err_msg,
-        std::vector<std::pair<region_base const*, std::string>> val,
-        std::vector<std::string> hints)
-{
-    return format_underline(err_msg, std::move(val), std::move(hints));
-}
-inline std::string format_error_impl(const std::string& err_msg,
-        std::vector<std::pair<region_base const*, std::string>> val)
-{
-    return format_underline(err_msg, std::move(val));
-}
-
-template<typename ... Ts>
-std::string format_error_impl(const std::string& err_msg,
-        std::vector<std::pair<region_base const*, std::string>> val,
         const toml::value& v, const std::string& comment,
-        Ts&& ... args)
+        std::vector<std::string> hints = {})
 {
-    val.push_back(std::make_pair(std::addressof(get_region(v)), comment));
+    return detail::format_underline(err_msg,
-    return format_error_impl(err_msg, std::move(val), std::forward<Ts>(args)...);
+        std::vector<std::pair<detail::region_base const*, std::string>>{
+            {std::addressof(detail::get_region(v)), comment}
+        }, std::move(hints));
 }
-} // detail
 
-template<typename ... Ts>
+inline std::string format_error(const std::string& err_msg,
-std::string format_error(const std::string& err_msg, Ts&& ... args)
+        const toml::value& v1, const std::string& comment1,
+        const toml::value& v2, const std::string& comment2,
+        std::vector<std::string> hints = {})
 {
-    std::vector<std::pair<detail::region_base const*, std::string>> val;
+    return detail::format_underline(err_msg,
-    val.reserve(sizeof...(args) / 2);
+        std::vector<std::pair<detail::region_base const*, std::string>>{
-    return detail::format_error_impl(err_msg, std::move(val),
+            {std::addressof(detail::get_region(v1)), comment1},
-                                     std::forward<Ts>(args)...);
+            {std::addressof(detail::get_region(v2)), comment2}
+        }, std::move(hints));
+}
+
+inline std::string format_error(const std::string& err_msg,
+        const toml::value& v1, const std::string& comment1,
+        const toml::value& v2, const std::string& comment2,
+        const toml::value& v3, const std::string& comment3,
+        std::vector<std::string> hints = {})
+{
+    return detail::format_underline(err_msg,
+        std::vector<std::pair<detail::region_base const*, std::string>>{
+            {std::addressof(detail::get_region(v1)), comment1},
+            {std::addressof(detail::get_region(v2)), comment2},
+            {std::addressof(detail::get_region(v3)), comment3}
+        }, std::move(hints));
 }
 
 template<typename Visitor>
@@ -877,7 +1001,7 @@ visit(Visitor&& visitor, toml::value& v)
 }
 
 template<typename Visitor>
-detail::return_type_of_t<Visitor, toml::boolean&>
+detail::return_type_of_t<Visitor, toml::boolean&&>
 visit(Visitor&& visitor, toml::value&& v)
 {
     switch(v.type())