fix: ctor of time and null

include/toml11/fwd/format_fwd.hpp

@@ -214,6 +214,29 @@ struct table_format_info
 bool operator==(const table_format_info&, const table_format_info&) noexcept;
 bool operator!=(const table_format_info&, const table_format_info&) noexcept;
 
+// ----------------------------------------------------------------------------
+// key
+
+enum class key_format : std::uint8_t
+{
+    bare           = 0,
+    quoted         = 1, // ""
+    quoted_literal = 2  // ''
+};
+
+std::ostream& operator<<(std::ostream& os, const key_format f);
+std::string to_string(const key_format);
+
+struct key_format_info
+{
+    key_format fmt = key_format::bare;
+    std::int32_t spaces_before_equal = 1;
+    std::int32_t spaces_after_equal  = 1;
+};
+
+bool operator==(const key_format_info&, const key_format_info&) noexcept;
+bool operator!=(const key_format_info&, const key_format_info&) noexcept;
+
 // ----------------------------------------------------------------------------
 // wrapper
 

include/toml11/impl/format_impl.hpp

@@ -293,5 +293,41 @@ TOML11_INLINE bool operator!=(const table_format_info& lhs, const table_format_i
     return !(lhs == rhs);
 }
 
+// ----------------------------------------------------------------------------
+// key
+
+TOML11_INLINE std::ostream& operator<<(std::ostream& os, const key_format f)
+{
+    switch(f)
+    {
+        case key_format::bare           : {os << "bare"          ; break;}
+        case key_format::quoted         : {os << "quoted"        ; break;}
+        case key_format::quoted_literal : {os << "quoted_literal"; break;}
+        default:
+        {
+            os << "unknown key_format: " << static_cast<std::uint8_t>(f);
+            break;
+        }
+    }
+    return os;
+}
+TOML11_INLINE std::string to_string(const key_format c)
+{
+    std::ostringstream oss;
+    oss << c;
+    return oss.str();
+}
+
+TOML11_INLINE bool operator==(const key_format_info& lhs, const key_format_info& rhs) noexcept
+{
+    return lhs.fmt                 == rhs.fmt                 &&
+           lhs.spaces_before_equal == rhs.spaces_before_equal &&
+           lhs.spaces_after_equal  == rhs.spaces_after_equal  ;
+}
+TOML11_INLINE bool operator!=(const key_format_info& lhs, const key_format_info& rhs) noexcept
+{
+    return !(lhs == rhs);
+}
+
 } // namespace toml
 #endif // TOML11_FORMAT_IMPL_HPP

include/toml11/parser.hpp

@@ -172,7 +172,7 @@ parse_boolean(location& loc, const context<TC>& ctx)
     // no format info for boolean
     boolean_format_info fmt;
 
-    return ok(basic_value<TC>(val, std::move(fmt), {}, std::move(reg)));
+    return ok(basic_value<TC>(val, std::move(fmt), {}, {}, std::move(reg)));
 }
 
 /* ============================================================================
@@ -221,7 +221,7 @@ parse_bin_integer(location& loc, const context<TC>& ctx)
     const auto val = TC::parse_int(str, source_location(region(loc)), 2);
     if(val.is_ok())
     {
-        return ok(basic_value<TC>(val.as_ok(), std::move(fmt), {}, std::move(reg)));
+        return ok(basic_value<TC>(val.as_ok(), std::move(fmt), {}, {}, std::move(reg)));
     }
     else
     {
@@ -273,7 +273,7 @@ parse_oct_integer(location& loc, const context<TC>& ctx)
     const auto val = TC::parse_int(str, source_location(region(loc)), 8);
     if(val.is_ok())
     {
-        return ok(basic_value<TC>(val.as_ok(), std::move(fmt), {}, std::move(reg)));
+        return ok(basic_value<TC>(val.as_ok(), std::move(fmt), {}, {}, std::move(reg)));
     }
     else
     {
@@ -331,7 +331,7 @@ parse_hex_integer(location& loc, const context<TC>& ctx)
     const auto val = TC::parse_int(str, source_location(region(loc)), 16);
     if(val.is_ok())
     {
-        return ok(basic_value<TC>(val.as_ok(), std::move(fmt), {}, std::move(reg)));
+        return ok(basic_value<TC>(val.as_ok(), std::move(fmt), {}, {}, std::move(reg)));
     }
     else
     {
@@ -402,7 +402,7 @@ parse_dec_integer(location& loc, const context<TC>& ctx)
         fmt.suffix = sfx;
     }
 
-    return ok(basic_value<TC>(val.as_ok(), std::move(fmt), {}, std::move(reg)));
+    return ok(basic_value<TC>(val.as_ok(), std::move(fmt), {}, {}, std::move(reg)));
 }
 
 template<typename TC>
@@ -667,7 +667,7 @@ parse_floating(location& loc, const context<TC>& ctx)
         fmt.suffix = sfx;
     }
 
-    return ok(basic_value<TC>(val, std::move(fmt), {}, std::move(reg)));
+    return ok(basic_value<TC>(val, std::move(fmt), {}, {}, std::move(reg)));
 }
 
 /* ============================================================================
@@ -785,7 +785,7 @@ parse_local_date(location& loc, const context<TC>& ctx)
     auto fmt = std::move(std::get<1>(val_fmt_reg.unwrap()));
     auto reg = std::move(std::get<2>(val_fmt_reg.unwrap()));
 
-    return ok(basic_value<TC>(std::move(val), std::move(fmt), {}, std::move(reg)));
+    return ok(basic_value<TC>(std::move(val), std::move(fmt), {}, {}, std::move(reg)));
 }
 
 // all the offset_datetime, local_datetime, local_time parses date part.
@@ -954,7 +954,7 @@ parse_local_time(location& loc, const context<TC>& ctx)
     auto fmt = std::move(std::get<1>(val_fmt_reg.unwrap()));
     auto reg = std::move(std::get<2>(val_fmt_reg.unwrap()));
 
-    return ok(basic_value<TC>(std::move(val), std::move(fmt), {}, std::move(reg)));
+    return ok(basic_value<TC>(std::move(val), std::move(fmt), {}, {}, std::move(reg)));
 }
 
 template<typename TC>
@@ -1013,7 +1013,7 @@ parse_local_datetime(location& loc, const context<TC>& ctx)
     local_datetime val(std::get<0>(date_fmt_reg.unwrap()),
                        std::get<0>(time_fmt_reg.unwrap()));
 
-    return ok(basic_value<TC>(val, std::move(fmt), {}, std::move(reg)));
+    return ok(basic_value<TC>(val, std::move(fmt), {}, {}, std::move(reg)));
 }
 
 template<typename TC>
@@ -1140,7 +1140,7 @@ parse_offset_datetime(location& loc, const context<TC>& ctx)
                                        std::get<0>(time_fmt_reg.unwrap())),
                                        offset);
 
-    return ok(basic_value<TC>(val, std::move(fmt), {}, std::move(reg)));
+    return ok(basic_value<TC>(val, std::move(fmt), {}, {}, std::move(reg)));
 }
 
 /* ============================================================================
@@ -1401,7 +1401,7 @@ parse_ml_basic_string(location& loc, const context<TC>& ctx)
     }
 
     return ok(basic_value<TC>(
-            std::move(val), std::move(fmt), {}, std::move(reg)
+            std::move(val), std::move(fmt), {}, {}, std::move(reg)
         ));
 }
 
@@ -1481,7 +1481,7 @@ parse_basic_string(location& loc, const context<TC>& ctx)
     auto val = std::move(val_res.unwrap().first );
     auto reg = std::move(val_res.unwrap().second);
 
-    return ok(basic_value<TC>(std::move(val), std::move(fmt), {}, std::move(reg)));
+    return ok(basic_value<TC>(std::move(val), std::move(fmt), {}, {}, std::move(reg)));
 }
 
 template<typename TC>
@@ -1528,7 +1528,7 @@ parse_ml_literal_string(location& loc, const context<TC>& ctx)
     string_type val(str.begin(), str.end());
 
     return ok(basic_value<TC>(
-            std::move(val), std::move(fmt), {}, std::move(reg)
+            std::move(val), std::move(fmt), {}, {}, std::move(reg)
         ));
 }
 
@@ -1581,7 +1581,7 @@ parse_literal_string(location& loc, const context<TC>& ctx)
     auto reg = std::move(val_res.unwrap().second);
 
     return ok(basic_value<TC>(
-            std::move(val), std::move(fmt), {}, std::move(reg)
+            std::move(val), std::move(fmt), {}, {}, std::move(reg)
         ));
 }
 
@@ -1793,6 +1793,9 @@ parse_key_value_pair(location& loc, context<TC>& ctx)
         // loc = first;
         return err(v_res.unwrap_err());
     }
+
+    // set key reg/fmt
+
     return ok(std::make_pair(std::move(key_res.unwrap()), std::move(v_res.unwrap())));
 }
 
@@ -2049,7 +2052,7 @@ parse_array(location& loc, context<TC>& ctx)
     }
 
     return ok(basic_value<TC>(
-            std::move(val), std::move(fmt), {}, region(first, loc)
+            std::move(val), std::move(fmt), {}, {}, region(first, loc)
         ));
 }
 
@@ -2206,7 +2209,7 @@ insert_value(const inserting_value_kind kind,
                     fmt.fmt = table_format::implicit;
                 }
                 current_table.emplace(key, value_type(
-                    table_type{}, fmt, std::vector<std::string>{}, key_reg));
+                    table_type{}, fmt, std::vector<std::string>{}, {}, key_reg));
 
                 assert(current_table.at(key).is_table());
                 current_table_ptr = std::addressof(current_table.at(key).as_table());
@@ -2353,7 +2356,8 @@ insert_value(const inserting_value_kind kind,
 
                         current_table.emplace(key, value_type(
                                 array_type{ std::move(val) }, std::move(fmt),
-                                std::vector<std::string>{}, std::move(key_reg)
+                                std::vector<std::string>{}, key_format_info{},
+                                key_reg, key_reg
                             ));
 
                         assert( ! current_table.at(key).as_array().empty());
@@ -2604,7 +2608,7 @@ parse_inline_table(location& loc, context<TC>& ctx)
     }
 
     basic_value<TC> retval(
-        std::move(table), std::move(fmt), {}, region(first, loc));
+        std::move(table), std::move(fmt), {}, {}, region(first, loc));
 
     return ok(std::move(retval));
 }
@@ -3171,10 +3175,10 @@ parse_file(location& loc, context<TC>& ctx)
 
     if(loc.eof())
     {
-        return ok(value_type(table_type(), table_format_info{}, {}, region(loc)));
+        return ok(value_type(table_type(), table_format_info{}, {}, {}, region(loc)));
     }
 
-    value_type root(table_type(), table_format_info{}, {}, region(loc));
+    value_type root(table_type(), table_format_info{}, {}, {}, region(loc));
     root.as_table_fmt().fmt = table_format::multiline;
     root.as_table_fmt().indent_type = indent_char::none;
 
@@ -3279,7 +3283,7 @@ parse_file(location& loc, context<TC>& ctx)
             table_format_info fmt;
             fmt.fmt = table_format::multiline;
             fmt.indent_type = indent_char::none;
-            auto tab = value_type(table_type{}, std::move(fmt), std::move(com), reg);
+            auto tab = value_type(table_type{}, std::move(fmt), std::move(com), {}, reg);
 
             auto inserted = insert_value(inserting_value_kind::array_table,
                 std::addressof(root.as_table()),
@@ -3366,7 +3370,7 @@ parse_file(location& loc, context<TC>& ctx)
             table_format_info fmt;
             fmt.fmt = table_format::multiline;
             fmt.indent_type = indent_char::none;
-            auto tab = value_type(table_type{}, std::move(fmt), std::move(com), reg);
+            auto tab = value_type(table_type{}, std::move(fmt), std::move(com), {}, reg);
 
             auto inserted = insert_value(inserting_value_kind::std_table,
                 std::addressof(root.as_table()),
@@ -3441,7 +3445,7 @@ parse_impl(std::vector<location::char_type> cs, std::string fname, const spec& s
     {
         auto src = std::make_shared<std::vector<location::char_type>>(std::move(cs));
         location loc(std::move(src), std::move(fname));
-        return ok(value_type(table_type(), table_format_info{}, std::vector<std::string>{}, region(loc)));
+        return ok(value_type(table_type(), table_format_info{}, std::vector<std::string>{}, {}, region(loc)));
     }
 
     // to simplify parser, add newline at the end if there is no LF.

include/toml11/value.hpp

@@ -53,6 +53,9 @@ error_info make_not_found_error(const basic_value<TC>&, const std::string&, cons
 template<typename TC>
 void change_region_of_value(basic_value<TC>&, const basic_value<TC>&);
 
+template<typename TC>
+void change_region_of_key(basic_value<TC>&, region);
+
 template<typename TC, value_t V>
 struct getter;
 } // detail
@@ -85,14 +88,14 @@ class basic_value
   public:
 
     basic_value() noexcept
-        : type_(value_t::empty), empty_('\0'), region_{}, comments_{}
+        : type_(value_t::empty), empty_('\0'), region_{}, comments_{}, key_region_{}, key_fmt_{}
     {}
     ~basic_value() noexcept {this->cleanup();}
 
     // copy/move constructor/assigner ===================================== {{{
 
     basic_value(const basic_value& v)
-        : type_(v.type_), region_(v.region_), comments_(v.comments_)
+        : type_(v.type_), region_(v.region_), comments_(v.comments_), key_region_(v.key_region_), key_fmt_(v.key_fmt_)
     {
         switch(this->type_)
         {
@@ -111,7 +114,8 @@ class basic_value
     }
     basic_value(basic_value&& v)
         : type_(v.type()), region_(std::move(v.region_)),
-          comments_(std::move(v.comments_))
+          comments_(std::move(v.comments_)),
+          key_region_(v.key_region_), key_fmt_(v.key_fmt_)
     {
         switch(this->type_)
         {
@@ -137,6 +141,8 @@ class basic_value
         this->type_     = v.type_;
         this->region_   = v.region_;
         this->comments_ = v.comments_;
+        this->key_region_ = v.key_region_;
+        this->key_fmt_    = v.key_fmt_;
         switch(this->type_)
         {
             case value_t::boolean        : assigner(boolean_        , v.boolean_        ); break;
@@ -161,6 +167,8 @@ class basic_value
         this->type_     = v.type_;
         this->region_   = std::move(v.region_);
         this->comments_ = std::move(v.comments_);
+        this->key_region_ = std::move(v.key_region_);
+        this->key_fmt_    = std::move(v.key_fmt_);
         switch(this->type_)
         {
             case value_t::boolean        : assigner(boolean_        , std::move(v.boolean_        )); break;
@@ -183,7 +191,8 @@ class basic_value
 
     basic_value(basic_value v, std::vector<std::string> com)
         : type_(v.type()), region_(std::move(v.region_)),
-          comments_(std::move(com))
+          comments_(std::move(com)),
+          key_region_(v.key_region_), key_fmt_(v.key_fmt_)
     {
         switch(this->type_)
         {
@@ -208,7 +217,9 @@ class basic_value
     basic_value(basic_value<TI> other)
         : type_(other.type_),
           region_(std::move(other.region_)),
-          comments_(std::move(other.comments_))
+          comments_(std::move(other.comments_)),
+          key_region_(std::move(other.key_region_)),
+          key_fmt_(std::move(other.key_fmt_))
     {
         switch(other.type_)
         {
@@ -253,7 +264,9 @@ class basic_value
     basic_value(basic_value<TI> other, std::vector<std::string> com)
         : type_(other.type_),
           region_(std::move(other.region_)),
-          comments_(std::move(com))
+          comments_(std::move(com)),
+          key_region_(std::move(other.key_region_)),
+          key_fmt_(std::move(other.key_fmt_))
     {
         switch(other.type_)
         {
@@ -297,9 +310,11 @@ class basic_value
     basic_value& operator=(basic_value<TI> other)
     {
         this->cleanup();
-        this->region_ = other.region_;
-        this->comments_    = comment_type(other.comments_);
-        this->type_        = other.type_;
+        this->region_     = other.region_;
+        this->comments_   = comment_type(other.comments_);
+        this->key_region_ = other.key_region_;
+        this->key_fmt_    = other.key_fmt_;
+        this->type_       = other.type_;
         switch(other.type_)
         {
             // use auto-convert in constructor
@@ -343,22 +358,18 @@ class basic_value
 
     // constructor (boolean) ============================================== {{{
 
-    basic_value(boolean_type x)
-        : basic_value(x, boolean_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(boolean_type x, boolean_format_info fmt)
-        : basic_value(x, fmt, std::vector<std::string>{}, region_type{})
-    {}
     basic_value(boolean_type x, std::vector<std::string> com)
-        : basic_value(x, boolean_format_info{}, std::move(com), region_type{})
+        : basic_value(x, boolean_format_info{}, std::move(com))
     {}
-    basic_value(boolean_type x, boolean_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, fmt, std::move(com), region_type{})
-    {}
-    basic_value(boolean_type x, boolean_format_info fmt,
-                std::vector<std::string> com, region_type reg)
+    basic_value(boolean_type x,
+                boolean_format_info      fmt = boolean_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
         : type_(value_t::boolean), boolean_(boolean_storage(x, fmt)),
-          region_(std::move(reg)), comments_(std::move(com))
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(key_reg), key_fmt_(key_fmt)
     {}
     basic_value& operator=(boolean_type x)
     {
@@ -370,6 +381,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::boolean;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->boolean_, boolean_storage(x, fmt));
         return *this;
     }
@@ -378,21 +390,19 @@ class basic_value
 
     // constructor (integer) ============================================== {{{
 
-    basic_value(integer_type x)
-        : basic_value(std::move(x), integer_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(integer_type x, integer_format_info fmt)
-        : basic_value(std::move(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     basic_value(integer_type x, std::vector<std::string> com)
-        : basic_value(std::move(x), integer_format_info{}, std::move(com), region_type{})
+        : basic_value(std::move(x), integer_format_info{}, std::move(com))
     {}
-    basic_value(integer_type x, integer_format_info fmt, std::vector<std::string> com)
-        : basic_value(std::move(x), std::move(fmt), std::move(com), region_type{})
-    {}
-    basic_value(integer_type x, integer_format_info fmt, std::vector<std::string> com, region_type reg)
-        : type_(value_t::integer), integer_(integer_storage(std::move(x), std::move(fmt))),
-          region_(std::move(reg)), comments_(std::move(com))
+    basic_value(integer_type             x,
+                integer_format_info      fmt = integer_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
+        : type_(value_t::integer),
+          integer_(integer_storage(std::move(x), std::move(fmt))),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(integer_type x)
     {
@@ -404,6 +414,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::integer;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->integer_, integer_storage(std::move(x), std::move(fmt)));
         return *this;
     }
@@ -419,26 +430,21 @@ class basic_value
 
   public:
 
-    template<typename T, enable_if_integer_like_t<T> = nullptr>
-    basic_value(T x)
-        : basic_value(std::move(x), integer_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    template<typename T, enable_if_integer_like_t<T> = nullptr>
-    basic_value(T x, integer_format_info fmt)
-        : basic_value(std::move(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     template<typename T, enable_if_integer_like_t<T> = nullptr>
     basic_value(T x, std::vector<std::string> com)
-        : basic_value(std::move(x), integer_format_info{}, std::move(com), region_type{})
+        : basic_value(std::move(x), integer_format_info{}, std::move(com))
     {}
     template<typename T, enable_if_integer_like_t<T> = nullptr>
-    basic_value(T x, integer_format_info fmt, std::vector<std::string> com)
-        : basic_value(std::move(x), std::move(fmt), std::move(com), region_type{})
-    {}
-    template<typename T, enable_if_integer_like_t<T> = nullptr>
-    basic_value(T x, integer_format_info fmt, std::vector<std::string> com, region_type reg)
-        : type_(value_t::integer), integer_(integer_storage(std::move(x), std::move(fmt))),
-          region_(std::move(reg)), comments_(std::move(com))
+    basic_value(T x,
+                integer_format_info      fmt = integer_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
+        : type_(value_t::integer),
+          integer_(integer_storage(std::move(x), std::move(fmt))),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     template<typename T, enable_if_integer_like_t<T> = nullptr>
     basic_value& operator=(T x)
@@ -451,6 +457,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::integer;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->integer_, integer_storage(x, std::move(fmt)));
         return *this;
     }
@@ -459,21 +466,19 @@ class basic_value
 
     // constructor (floating) ============================================= {{{
 
-    basic_value(floating_type x)
-        : basic_value(std::move(x), floating_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(floating_type x, floating_format_info fmt)
-        : basic_value(std::move(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     basic_value(floating_type x, std::vector<std::string> com)
-        : basic_value(std::move(x), floating_format_info{}, std::move(com), region_type{})
+        : basic_value(std::move(x), floating_format_info{}, std::move(com))
     {}
-    basic_value(floating_type x, floating_format_info fmt, std::vector<std::string> com)
-        : basic_value(std::move(x), std::move(fmt), std::move(com), region_type{})
-    {}
-    basic_value(floating_type x, floating_format_info fmt, std::vector<std::string> com, region_type reg)
-        : type_(value_t::floating), floating_(floating_storage(std::move(x), std::move(fmt))),
-          region_(std::move(reg)), comments_(std::move(com))
+    basic_value(floating_type x,
+                floating_format_info     fmt = floating_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
+        : type_(value_t::floating),
+          floating_(floating_storage(std::move(x), std::move(fmt))),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(floating_type x)
     {
@@ -485,6 +490,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::floating;
         this->region_ = region_type{};
+        // key_region/fmt is kept
         assigner(this->floating_, floating_storage(std::move(x), std::move(fmt)));
         return *this;
     }
@@ -499,32 +505,22 @@ class basic_value
 
   public:
 
-    template<typename T, enable_if_floating_like_t<T> = nullptr>
-    basic_value(T x)
-        : basic_value(x, floating_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-
-    template<typename T, enable_if_floating_like_t<T> = nullptr>
-    basic_value(T x, floating_format_info fmt)
-        : basic_value(x, std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
-
     template<typename T, enable_if_floating_like_t<T> = nullptr>
     basic_value(T x, std::vector<std::string> com)
-        : basic_value(x, floating_format_info{}, std::move(com), region_type{})
+        : basic_value(x, floating_format_info{}, std::move(com))
     {}
-
     template<typename T, enable_if_floating_like_t<T> = nullptr>
-    basic_value(T x, floating_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, std::move(fmt), std::move(com), region_type{})
+    basic_value(T x,
+                floating_format_info     fmt = floating_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
+        : type_(value_t::floating),
+          floating_(floating_storage(x, std::move(fmt))),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
-
-    template<typename T, enable_if_floating_like_t<T> = nullptr>
-    basic_value(T x, floating_format_info fmt, std::vector<std::string> com, region_type reg)
-        : type_(value_t::floating), floating_(floating_storage(x, std::move(fmt))),
-          region_(std::move(reg)), comments_(std::move(com))
-    {}
-
     template<typename T, enable_if_floating_like_t<T> = nullptr>
     basic_value& operator=(T x)
     {
@@ -536,6 +532,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::floating;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->floating_, floating_storage(x, std::move(fmt)));
         return *this;
     }
@@ -544,22 +541,19 @@ class basic_value
 
     // constructor (string) =============================================== {{{
 
-    basic_value(string_type x)
-        : basic_value(std::move(x), string_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(string_type x, string_format_info fmt)
-        : basic_value(std::move(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     basic_value(string_type x, std::vector<std::string> com)
-        : basic_value(std::move(x), string_format_info{}, std::move(com), region_type{})
+        : basic_value(std::move(x), string_format_info{}, std::move(com))
     {}
-    basic_value(string_type x, string_format_info fmt, std::vector<std::string> com)
-        : basic_value(std::move(x), std::move(fmt), std::move(com), region_type{})
-    {}
-    basic_value(string_type x, string_format_info fmt,
-                std::vector<std::string> com, region_type reg)
-        : type_(value_t::string), string_(string_storage(std::move(x), std::move(fmt))),
-          region_(std::move(reg)), comments_(std::move(com))
+    basic_value(string_type x,
+                string_format_info       fmt = string_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
+        : type_(value_t::string),
+          string_(string_storage(std::move(x), std::move(fmt))),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(string_type x)
     {
@@ -571,28 +565,26 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::string;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->string_, string_storage(x, std::move(fmt)));
         return *this;
     }
 
     // "string literal"
 
-    basic_value(const typename string_type::value_type* x)
-        : basic_value(x, string_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(const typename string_type::value_type* x, string_format_info fmt)
-        : basic_value(x, std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     basic_value(const typename string_type::value_type* x, std::vector<std::string> com)
-        : basic_value(x, string_format_info{}, std::move(com), region_type{})
+        : basic_value(x, string_format_info{}, std::move(com))
     {}
-    basic_value(const typename string_type::value_type* x, string_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, std::move(fmt), std::move(com), region_type{})
-    {}
-    basic_value(const typename string_type::value_type* x, string_format_info fmt,
-                std::vector<std::string> com, region_type reg)
-        : type_(value_t::string), string_(string_storage(string_type(x), std::move(fmt))),
-          region_(std::move(reg)), comments_(std::move(com))
+    basic_value(const typename string_type::value_type* x,
+                string_format_info       fmt = string_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
+        : type_(value_t::string),
+          string_(string_storage(string_type(x), std::move(fmt))),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(const typename string_type::value_type* x)
     {
@@ -604,6 +596,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::string;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->string_, string_storage(string_type(x), std::move(fmt)));
         return *this;
     }
@@ -612,22 +605,18 @@ class basic_value
     using string_view_type = std::basic_string_view<
         typename string_type::value_type, typename string_type::traits_type>;
 
-    basic_value(string_view_type x)
-        : basic_value(x, string_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(string_view_type x, string_format_info fmt)
-        : basic_value(x, std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     basic_value(string_view_type x, std::vector<std::string> com)
-        : basic_value(x, string_format_info{}, std::move(com), region_type{})
+        : basic_value(x, string_format_info{}, std::move(com))
     {}
-    basic_value(string_view_type x, string_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, std::move(fmt), std::move(com), region_type{})
-    {}
-    basic_value(string_view_type x, string_format_info fmt,
-                std::vector<std::string> com, region_type reg)
+    basic_value(string_view_type x,
+                string_format_info       fmt = string_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
         : type_(value_t::string), string_(string_storage(string_type(x), std::move(fmt))),
-          region_(std::move(reg)), comments_(std::move(com))
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(string_view_type x)
     {
@@ -639,49 +628,34 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::string;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->string_, string_storage(string_type(x), std::move(fmt)));
         return *this;
     }
 
 #endif // TOML11_HAS_STRING_VIEW
 
-    template<typename T, cxx::enable_if_t<cxx::conjunction<
-            cxx::negation<std::is_same<cxx::remove_cvref_t<T>, string_type>>,
-            detail::is_1byte_std_basic_string<T>
-        >::value, std::nullptr_t> = nullptr>
-    basic_value(const T& x)
-        : basic_value(x, string_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    template<typename T, cxx::enable_if_t<cxx::conjunction<
-            cxx::negation<std::is_same<cxx::remove_cvref_t<T>, string_type>>,
-            detail::is_1byte_std_basic_string<T>
-        >::value, std::nullptr_t> = nullptr>
-    basic_value(const T& x, string_format_info fmt)
-        : basic_value(x, std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     template<typename T, cxx::enable_if_t<cxx::conjunction<
             cxx::negation<std::is_same<cxx::remove_cvref_t<T>, string_type>>,
             detail::is_1byte_std_basic_string<T>
         >::value, std::nullptr_t> = nullptr>
     basic_value(const T& x, std::vector<std::string> com)
-        : basic_value(x, string_format_info{}, std::move(com), region_type{})
+        : basic_value(x, string_format_info{}, std::move(com))
     {}
     template<typename T, cxx::enable_if_t<cxx::conjunction<
             cxx::negation<std::is_same<cxx::remove_cvref_t<T>, string_type>>,
             detail::is_1byte_std_basic_string<T>
         >::value, std::nullptr_t> = nullptr>
-    basic_value(const T& x, string_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, std::move(fmt), std::move(com), region_type{})
-    {}
-    template<typename T, cxx::enable_if_t<cxx::conjunction<
-            cxx::negation<std::is_same<cxx::remove_cvref_t<T>, string_type>>,
-            detail::is_1byte_std_basic_string<T>
-        >::value, std::nullptr_t> = nullptr>
-    basic_value(const T& x, string_format_info fmt,
-                std::vector<std::string> com, region_type reg)
+    basic_value(const T& x,
+                string_format_info       fmt = string_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
         : type_(value_t::string),
           string_(string_storage(detail::string_conv<string_type>(x), std::move(fmt))),
-          region_(std::move(reg)), comments_(std::move(com))
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     template<typename T, cxx::enable_if_t<cxx::conjunction<
             cxx::negation<std::is_same<cxx::remove_cvref_t<T>, string_type>>,
@@ -697,6 +671,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::string;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->string_, string_storage(detail::string_conv<string_type>(x), std::move(fmt)));
         return *this;
     }
@@ -705,22 +680,19 @@ class basic_value
 
     // constructor (local_date) =========================================== {{{
 
-    basic_value(local_date_type x)
-        : basic_value(x, local_date_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(local_date_type x, local_date_format_info fmt)
-        : basic_value(x, fmt, std::vector<std::string>{}, region_type{})
-    {}
     basic_value(local_date_type x, std::vector<std::string> com)
-        : basic_value(x, local_date_format_info{}, std::move(com), region_type{})
+        : basic_value(x, local_date_format_info{}, std::move(com))
     {}
-    basic_value(local_date_type x, local_date_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, fmt, std::move(com), region_type{})
-    {}
-    basic_value(local_date_type x, local_date_format_info fmt,
-                std::vector<std::string> com, region_type reg)
-        : type_(value_t::local_date), local_date_(local_date_storage(x, fmt)),
-          region_(std::move(reg)), comments_(std::move(com))
+    basic_value(local_date_type x,
+                local_date_format_info   fmt = local_date_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
+        : type_(value_t::local_date),
+          local_date_(local_date_storage(x, fmt)),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(local_date_type x)
     {
@@ -732,6 +704,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::local_date;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->local_date_, local_date_storage(x, fmt));
         return *this;
     }
@@ -740,22 +713,18 @@ class basic_value
 
     // constructor (local_time) =========================================== {{{
 
-    basic_value(local_time_type x)
-        : basic_value(x, local_time_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(local_time_type x, local_time_format_info fmt)
-        : basic_value(x, fmt, std::vector<std::string>{}, region_type{})
-    {}
     basic_value(local_time_type x, std::vector<std::string> com)
-        : basic_value(x, local_time_format_info{}, std::move(com), region_type{})
+        : basic_value(x, local_time_format_info{}, std::move(com))
     {}
-    basic_value(local_time_type x, local_time_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, fmt, std::move(com), region_type{})
-    {}
-    basic_value(local_time_type x, local_time_format_info fmt,
-                std::vector<std::string> com, region_type reg)
+    basic_value(local_time_type x,
+                local_time_format_info   fmt = local_time_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
         : type_(value_t::local_time), local_time_(local_time_storage(x, fmt)),
-          region_(std::move(reg)), comments_(std::move(com))
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(local_time_type x)
     {
@@ -767,31 +736,24 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::local_time;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->local_time_, local_time_storage(x, fmt));
         return *this;
     }
 
-    template<typename Rep, typename Period>
-    basic_value(const std::chrono::duration<Rep, Period>& x)
-        : basic_value(local_time_type(x), local_time_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    template<typename Rep, typename Period>
-    basic_value(const std::chrono::duration<Rep, Period>& x, local_time_format_info fmt)
-        : basic_value(local_time_type(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     template<typename Rep, typename Period>
     basic_value(const std::chrono::duration<Rep, Period>& x, std::vector<std::string> com)
-        : basic_value(local_time_type(x), local_time_format_info{}, std::move(com), region_type{})
-    {}
-    template<typename Rep, typename Period>
-    basic_value(const std::chrono::duration<Rep, Period>& x, local_time_format_info fmt, std::vector<std::string> com)
-        : basic_value(local_time_type(x), std::move(fmt), std::move(com), region_type{})
+        : basic_value(local_time_type(x), local_time_format_info{}, std::move(com))
     {}
     template<typename Rep, typename Period>
     basic_value(const std::chrono::duration<Rep, Period>& x,
-                local_time_format_info fmt,
-                std::vector<std::string> com, region_type reg)
-        : basic_value(local_time_type(x), std::move(fmt), std::move(com), std::move(reg))
+                local_time_format_info   fmt = local_time_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
+        : basic_value(local_time_type(x), std::move(fmt), std::move(com), std::move(key_fmt),
+                      std::move(reg), std::move(key_reg))
     {}
     template<typename Rep, typename Period>
     basic_value& operator=(const std::chrono::duration<Rep, Period>& x)
@@ -804,6 +766,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::local_time;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->local_time_, local_time_storage(local_time_type(x), std::move(fmt)));
         return *this;
     }
@@ -812,22 +775,19 @@ class basic_value
 
     // constructor (local_datetime) =========================================== {{{
 
-    basic_value(local_datetime_type x)
-        : basic_value(x, local_datetime_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(local_datetime_type x, local_datetime_format_info fmt)
-        : basic_value(x, fmt, std::vector<std::string>{}, region_type{})
-    {}
     basic_value(local_datetime_type x, std::vector<std::string> com)
-        : basic_value(x, local_datetime_format_info{}, std::move(com), region_type{})
+        : basic_value(x, local_datetime_format_info{}, std::move(com))
     {}
-    basic_value(local_datetime_type x, local_datetime_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, fmt, std::move(com), region_type{})
-    {}
-    basic_value(local_datetime_type x, local_datetime_format_info fmt,
-                std::vector<std::string> com, region_type reg)
-        : type_(value_t::local_datetime), local_datetime_(local_datetime_storage(x, fmt)),
-          region_(std::move(reg)), comments_(std::move(com))
+    basic_value(local_datetime_type x,
+                local_datetime_format_info fmt = local_datetime_format_info{},
+                std::vector<std::string>   com = {},
+                key_format_info        key_fmt = key_format_info{},
+                region_type                reg = region_type{},
+                region_type            key_reg = region_type{})
+        : type_(value_t::local_datetime),
+          local_datetime_(local_datetime_storage(x, fmt)),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(local_datetime_type x)
     {
@@ -839,6 +799,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::local_datetime;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->local_datetime_, local_datetime_storage(x, fmt));
         return *this;
     }
@@ -847,22 +808,19 @@ class basic_value
 
     // constructor (offset_datetime) =========================================== {{{
 
-    basic_value(offset_datetime_type x)
-        : basic_value(x, offset_datetime_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(offset_datetime_type x, offset_datetime_format_info fmt)
-        : basic_value(x, fmt, std::vector<std::string>{}, region_type{})
-    {}
     basic_value(offset_datetime_type x, std::vector<std::string> com)
-        : basic_value(x, offset_datetime_format_info{}, std::move(com), region_type{})
+        : basic_value(x, offset_datetime_format_info{}, std::move(com))
     {}
-    basic_value(offset_datetime_type x, offset_datetime_format_info fmt, std::vector<std::string> com)
-        : basic_value(x, fmt, std::move(com), region_type{})
-    {}
-    basic_value(offset_datetime_type x, offset_datetime_format_info fmt,
-                std::vector<std::string> com, region_type reg)
-        : type_(value_t::offset_datetime), offset_datetime_(offset_datetime_storage(x, fmt)),
-          region_(std::move(reg)), comments_(std::move(com))
+    basic_value(offset_datetime_type x,
+                offset_datetime_format_info fmt = offset_datetime_format_info{},
+                std::vector<std::string>    com = {},
+                key_format_info         key_fmt = key_format_info{},
+                region_type                 reg = region_type{},
+                region_type             key_reg = region_type{})
+        : type_(value_t::offset_datetime),
+          offset_datetime_(offset_datetime_storage(x, fmt)),
+          region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(offset_datetime_type x)
     {
@@ -874,27 +832,24 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::offset_datetime;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->offset_datetime_, offset_datetime_storage(x, fmt));
         return *this;
     }
 
     // system_clock::time_point
 
-    basic_value(std::chrono::system_clock::time_point x)
-        : basic_value(offset_datetime_type(x), offset_datetime_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(std::chrono::system_clock::time_point x, offset_datetime_format_info fmt)
-        : basic_value(offset_datetime_type(x), fmt, std::vector<std::string>{}, region_type{})
-    {}
     basic_value(std::chrono::system_clock::time_point x, std::vector<std::string> com)
-        : basic_value(offset_datetime_type(x), offset_datetime_format_info{}, std::move(com), region_type{})
+        : basic_value(offset_datetime_type(x), offset_datetime_format_info{}, std::move(com))
     {}
-    basic_value(std::chrono::system_clock::time_point x, offset_datetime_format_info fmt, std::vector<std::string> com)
-        : basic_value(offset_datetime_type(x), fmt, std::move(com), region_type{})
-    {}
-    basic_value(std::chrono::system_clock::time_point x, offset_datetime_format_info fmt,
-                std::vector<std::string> com, region_type reg)
-        : basic_value(offset_datetime_type(x), std::move(fmt), std::move(com), std::move(reg))
+    basic_value(std::chrono::system_clock::time_point x,
+                offset_datetime_format_info fmt = offset_datetime_format_info{},
+                std::vector<std::string>    com = {},
+                key_format_info         key_fmt = key_format_info{},
+                region_type                 reg = region_type{},
+                region_type             key_reg = region_type{})
+        : basic_value(offset_datetime_type(x), std::move(fmt), std::move(com),
+                      std::move(key_fmt), std::move(reg), std::move(key_reg))
     {}
     basic_value& operator=(std::chrono::system_clock::time_point x)
     {
@@ -906,6 +861,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::offset_datetime;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->offset_datetime_, offset_datetime_storage(offset_datetime_type(x), fmt));
         return *this;
     }
@@ -914,23 +870,19 @@ class basic_value
 
     // constructor (array) ================================================ {{{
 
-    basic_value(array_type x)
-        : basic_value(std::move(x), array_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(array_type x, array_format_info fmt)
-        : basic_value(std::move(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     basic_value(array_type x, std::vector<std::string> com)
-        : basic_value(std::move(x), array_format_info{}, std::move(com), region_type{})
+        : basic_value(std::move(x), array_format_info{}, std::move(com))
     {}
-    basic_value(array_type x, array_format_info fmt, std::vector<std::string> com)
-        : basic_value(std::move(x), fmt, std::move(com), region_type{})
-    {}
-    basic_value(array_type x, array_format_info fmt,
-                std::vector<std::string> com, region_type reg)
+    basic_value(array_type x,
+                array_format_info        fmt = array_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
         : type_(value_t::array), array_(array_storage(
               detail::storage<array_type>(std::move(x)), std::move(fmt)
-          )), region_(std::move(reg)), comments_(std::move(com))
+          )), region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(array_type x)
     {
@@ -942,6 +894,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::array;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->array_, array_storage(
                     detail::storage<array_type>(std::move(x)), std::move(fmt)));
         return *this;
@@ -963,31 +916,24 @@ class basic_value
 
   public:
 
-    template<typename T, enable_if_array_like_t<T> = nullptr>
-    basic_value(T x)
-        : basic_value(std::move(x), array_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    template<typename T, enable_if_array_like_t<T> = nullptr>
-    basic_value(T x, array_format_info fmt)
-        : basic_value(std::move(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     template<typename T, enable_if_array_like_t<T> = nullptr>
     basic_value(T x, std::vector<std::string> com)
-        : basic_value(std::move(x), array_format_info{}, std::move(com), region_type{})
+        : basic_value(std::move(x), array_format_info{}, std::move(com))
     {}
     template<typename T, enable_if_array_like_t<T> = nullptr>
-    basic_value(T x, array_format_info fmt, std::vector<std::string> com)
-        : basic_value(std::move(x), fmt, std::move(com), region_type{})
-    {}
-    template<typename T, enable_if_array_like_t<T> = nullptr>
-    basic_value(T x, array_format_info fmt,
-                std::vector<std::string> com, region_type reg)
+    basic_value(T x,
+                array_format_info        fmt = array_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
         : type_(value_t::array), array_(array_storage(
               detail::storage<array_type>(array_type(
                       std::make_move_iterator(x.begin()),
                       std::make_move_iterator(x.end()))
               ), std::move(fmt)
-          )), region_(std::move(reg)), comments_(std::move(com))
+          )), region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     template<typename T, enable_if_array_like_t<T> = nullptr>
     basic_value& operator=(T x)
@@ -1000,6 +946,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::array;
         this->region_ = region_type{};
+        // key region/fmt is kept
 
         array_type a(std::make_move_iterator(x.begin()),
                      std::make_move_iterator(x.end()));
@@ -1012,23 +959,19 @@ class basic_value
 
     // constructor (table) ================================================ {{{
 
-    basic_value(table_type x)
-        : basic_value(std::move(x), table_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    basic_value(table_type x, table_format_info fmt)
-        : basic_value(std::move(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     basic_value(table_type x, std::vector<std::string> com)
-        : basic_value(std::move(x), table_format_info{}, std::move(com), region_type{})
+        : basic_value(std::move(x), table_format_info{}, std::move(com))
     {}
-    basic_value(table_type x, table_format_info fmt, std::vector<std::string> com)
-        : basic_value(std::move(x), fmt, std::move(com), region_type{})
-    {}
-    basic_value(table_type x, table_format_info fmt,
-                std::vector<std::string> com, region_type reg)
+    basic_value(table_type x,
+                table_format_info        fmt = table_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
         : type_(value_t::table), table_(table_storage(
                 detail::storage<table_type>(std::move(x)), std::move(fmt)
-          )), region_(std::move(reg)), comments_(std::move(com))
+          )), region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     basic_value& operator=(table_type x)
     {
@@ -1040,6 +983,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::table;
         this->region_ = region_type{};
+        // key region/fmt is kept
         assigner(this->table_, table_storage(
             detail::storage<table_type>(std::move(x)), std::move(fmt)));
         return *this;
@@ -1059,31 +1003,24 @@ class basic_value
 
   public:
 
-    template<typename T, enable_if_table_like_t<T> = nullptr>
-    basic_value(T x)
-        : basic_value(std::move(x), table_format_info{}, std::vector<std::string>{}, region_type{})
-    {}
-    template<typename T, enable_if_table_like_t<T> = nullptr>
-    basic_value(T x, table_format_info fmt)
-        : basic_value(std::move(x), std::move(fmt), std::vector<std::string>{}, region_type{})
-    {}
     template<typename T, enable_if_table_like_t<T> = nullptr>
     basic_value(T x, std::vector<std::string> com)
-        : basic_value(std::move(x), table_format_info{}, std::move(com), region_type{})
+        : basic_value(std::move(x), table_format_info{}, std::move(com))
     {}
     template<typename T, enable_if_table_like_t<T> = nullptr>
-    basic_value(T x, table_format_info fmt, std::vector<std::string> com)
-        : basic_value(std::move(x), fmt, std::move(com), region_type{})
-    {}
-    template<typename T, enable_if_table_like_t<T> = nullptr>
-    basic_value(T x, table_format_info fmt,
-                std::vector<std::string> com, region_type reg)
+    basic_value(T x,
+                table_format_info        fmt = table_format_info{},
+                std::vector<std::string> com = {},
+                key_format_info      key_fmt = key_format_info{},
+                region_type              reg = region_type{},
+                region_type          key_reg = region_type{})
         : type_(value_t::table), table_(table_storage(
               detail::storage<table_type>(table_type(
                       std::make_move_iterator(x.begin()),
                       std::make_move_iterator(x.end())
               )), std::move(fmt)
-          )), region_(std::move(reg)), comments_(std::move(com))
+          )), region_(std::move(reg)), comments_(std::move(com)),
+          key_region_(std::move(key_reg)), key_fmt_(std::move(key_fmt))
     {}
     template<typename T, enable_if_table_like_t<T> = nullptr>
     basic_value& operator=(T x)
@@ -1096,6 +1033,7 @@ class basic_value
         this->cleanup();
         this->type_   = value_t::table;
         this->region_ = region_type{};
+        // key region/fmt is kept
 
         table_type t(std::make_move_iterator(x.begin()),
                      std::make_move_iterator(x.end()));
@@ -1180,7 +1118,8 @@ class basic_value
 
     // mainly for `null` extension
     basic_value(detail::none_t, region_type reg) noexcept
-        : type_(value_t::empty), empty_('\0'), region_(std::move(reg)), comments_{}
+        : type_(value_t::empty), empty_('\0'), region_(std::move(reg)), comments_{},
+          key_region_{}, key_fmt_{}
     {}
 
     // }}}
@@ -1856,6 +1795,13 @@ class basic_value
     comment_type const& comments() const noexcept {return this->comments_;}
     comment_type&       comments()       noexcept {return this->comments_;}
 
+    source_location key_location() const
+    {
+        return source_location(this->key_region_);
+    }
+    key_format_info&       key_fmt()       noexcept {return this->key_fmt_;}
+    key_format_info const& key_fmt() const noexcept {return this->key_fmt_;}
+
   private:
 
     // private helper functions =========================================== {{{
@@ -1905,6 +1851,9 @@ class basic_value
     template<typename TC>
     friend void detail::change_region_of_value(basic_value<TC>&, const basic_value<TC>&);
 
+    template<typename TC>
+    friend void change_region_of_key(basic_value<TC>&, detail::region);
+
     template<typename TC>
     friend class basic_value;
 
@@ -1940,8 +1889,10 @@ class basic_value
         array_storage           array_;
         table_storage           table_;
     };
-    region_type  region_;
-    comment_type comments_;
+    region_type     region_;
+    comment_type    comments_;
+    region_type     key_region_;
+    key_format_info key_fmt_;
 };
 
 template<typename TC>
@@ -2248,7 +2199,14 @@ TOML11_DETAIL_GENERATE_COMPTIME_GETTER(table          )
 template<typename TC>
 void change_region_of_value(basic_value<TC>& dst, const basic_value<TC>& src)
 {
-    dst.region_ = std::move(src.region_);
+    dst.region_     = std::move(src.region_);
+    dst.key_region_ = std::move(src.key_region_);
+    return;
+}
+template<typename TC>
+void change_region_of_key(basic_value<TC>& dst, region src)
+{
+    dst.key_region_ = std::move(src);
     return;
 }
 

include/toml_fwd.hpp

@@ -40,6 +40,7 @@ enum class string_format : std::uint8_t;
 enum class datetime_delimiter_kind : std::uint8_t;
 enum class array_format : std::uint8_t;
 enum class table_format : std::uint8_t;
+enum class key_format : std::uint8_t;
 
 struct boolean_format_info;
 struct integer_format_info;
@@ -51,6 +52,7 @@ struct local_date_format_info;
 struct local_time_format_info;
 struct array_format_info;
 struct table_format_info;
+struct key_format_info;
 
 template<typename Key, typename Val, typename Cmp, typename Allocator>
 class ordered_map;