From b8d3038d383a4caf93df054badf70181f4e8447c Mon Sep 17 00:00:00 2001
From: ToruNiina <niina.toru.68u@gmail.com>
Date: Sat, 1 Jun 2019 16:03:26 +0900
Subject: [PATCH] feat: add meta function to detect conversions

---
 toml/types.hpp | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/toml/types.hpp b/toml/types.hpp
index f15e955..2c0d9d8 100644
--- a/toml/types.hpp
+++ b/toml/types.hpp
@@ -139,6 +139,59 @@ template<typename T, typename V> struct is_exact_toml_type<T const&, V>
 template<typename T, typename V> struct is_exact_toml_type<T volatile&, V>      : is_exact_toml_type<T, V>{};
 template<typename T, typename V> struct is_exact_toml_type<T const volatile&, V>: is_exact_toml_type<T, V>{};
 
+// meta-function that check type T is convertible to toml::* types
+template<typename T, typename Value>
+struct is_convertible_to_toml_value : disjunction<
+    std::is_same<T, boolean>,                    // T is bool or
+    std::is_integral<T>,                         // T is an integer or
+    std::is_floating_point<T>,                   // T is a floating point or
+    std::is_same<T, std::string>,                // T is std::string or
+    std::is_same<T, toml::string>,               // T is toml::string or
+    is_string_literal<T>,                        // T is "string literal" or
+    std::is_same<T, toml::local_date>,           // T is local_date or
+    std::is_same<T, toml::local_time>,           // T is local_time or
+    std::is_same<T, toml::local_datetime>,       // T is local_datetime or
+    std::is_same<T, toml::offset_datetime>,      // T is offset_datetime or
+    std::is_same<T, std::chrono::system_clock::time_point> // T is time_point or
+    is_chrono_duration<T>,                       // T is a duration or
+    std::is_same<T, typename Value::array_type>, // T is an array type or
+    std::is_same<T, typename Value::table_type>, // T is an array type or
+    >{}
+
+// meta-function that returns value_t that represent the convertible type
+template<typename T, typename Value>
+struct convertible_toml_type_of : typename std::conditional<
+    /* if   */ is_exact_toml_type<T, Value>::value,
+    /* then */ value_t_constant<type_to_enum<T, Value>::value>,
+    /* else */ typename std::conditional<
+    // ----------------------------------------------------------------------
+    /* if   */ std::is_integral<T>::value,
+    /* then */ value_t_constant<value_t::integer>,
+    /* else */ typename std::conditional<
+    // ----------------------------------------------------------------------
+    /* if   */ std::is_floating_point<T>::value,
+    /* then */ value_t_constant<value_t::floating>,
+    /* else */ typename std::conditional<
+    // ----------------------------------------------------------------------
+    /* if   */ std::is_same<std::string>::value,
+    /* then */ value_t_constant<value_t::string>,
+    /* else */ typename std::conditional<
+    // ----------------------------------------------------------------------
+    /* if   */ is_string_literal<T>,
+    /* then */ value_t_constant<value_t::string>,
+    /* else */ typename std::conditional<
+    // ----------------------------------------------------------------------
+    /* if   */ is_chrono_duration<T>,
+    /* then */ value_t_constant<value_t::local_time>,
+    /* else */ typename std::conditional<
+    // ----------------------------------------------------------------------
+    /* if   */ std::is_same<T, std::chrono::system_clock::time_point>,
+    /* then */ value_t_constant<value_t::offset_datetime>,
+    /* else */ value_t_constant<value_t::empty>,
+    // ----------------------------------------------------------------------
+    >::type>::type>::type>::type>::type>::type>::type
+    >{}
+
 } // detail
 } // toml
 #endif// TOML11_TYPES_H