improved support for using enums with value_or()

CHANGELOG.md

@@ -33,6 +33,10 @@ template:
 -   fixed `for_each()` compilation error on GCC <= 7 (#197) (@sagi-ottopia, @damirbarr)
 -   fixed `FLT_RADIX` check getting broken by Intel MKL headers (#202) (@iago-lito)
 
+#### Additions
+
+-   improved support for using enums with `value_or()`
+
 #### Changes:
 
 -   renamed header files to have `.hpp` extension (`toml.h` is still present for backwards-compatibility)

include/toml++/impl/forward_declarations.hpp

@@ -476,10 +476,22 @@ TOML_IMPL_NAMESPACE_START
 	template <typename T, typename... U>
 	inline constexpr bool first_is_same<T, T, U...> = true;
 
+	template <typename T, bool = std::is_enum_v<T>>
+	struct underlying_type_
+	{
+		using type = std::underlying_type_t<T>;
+	};
+	template <typename T>
+	struct underlying_type_<T, false>
+	{
+		using type = T;
+	};
+	template <typename T>
+	using underlying_type = typename underlying_type_<T>::type;
+
 	// general value traits
 	// (as they relate to their equivalent native TOML type)
-	template <typename T>
+	struct default_value_traits
-	struct value_traits
 	{
 		using native_type										  = void;
 		static constexpr bool is_native							  = false;
@@ -489,6 +501,27 @@ TOML_IMPL_NAMESPACE_START
 		static constexpr auto type								  = node_type::none;
 	};
 
+	template <typename T>
+	struct value_traits;
+
+	template <typename T, bool = std::is_enum_v<T>>
+	struct value_traits_base_selector
+	{
+		static_assert(!is_cvref<T>);
+
+		using type = default_value_traits;
+	};
+	template <typename T>
+	struct value_traits_base_selector<T, true>
+	{
+		static_assert(!is_cvref<T>);
+
+		using type = value_traits<underlying_type<T>>;
+	};
+
+	template <typename T>
+	struct value_traits : value_traits_base_selector<T>::type
+	{};
 	template <typename T>
 	struct value_traits<const T> : value_traits<T>
 	{};
@@ -509,22 +542,23 @@ TOML_IMPL_NAMESPACE_START
 	template <typename T>
 	struct integer_limits
 	{
-		static constexpr auto min = (std::numeric_limits<T>::min)();
+		static constexpr T min = T{ (std::numeric_limits<underlying_type<T>>::min)() };
-		static constexpr auto max = (std::numeric_limits<T>::max)();
+		static constexpr T max = T{ (std::numeric_limits<underlying_type<T>>::max)() };
 	};
 	template <typename T>
 	struct integer_traits_base : integer_limits<T>
 	{
 		using native_type				= int64_t;
-		static constexpr bool is_native = std::is_same_v<T, native_type>;
+		static constexpr bool is_native = std::is_same_v<underlying_type<T>, native_type>;
-		static constexpr bool is_signed = static_cast<T>(-1) < T{}; // for impls not specializing std::is_signed<T>
+		static constexpr bool is_signed = static_cast<underlying_type<T>>(-1) < underlying_type<T>{};
 		static constexpr auto type		= node_type::integer;
 		static constexpr bool can_partially_represent_native = true;
 	};
 	template <typename T>
 	struct unsigned_integer_traits : integer_traits_base<T>
 	{
-		static constexpr bool is_losslessly_convertible_to_native = integer_limits<T>::max <= 9223372036854775807ULL;
+		static constexpr bool is_losslessly_convertible_to_native =
+			integer_limits<underlying_type<T>>::max <= 9223372036854775807ULL;
 		static constexpr bool can_represent_native = false;
 	};
 	template <typename T>
@@ -532,9 +566,11 @@ TOML_IMPL_NAMESPACE_START
 	{
 		using native_type = int64_t;
 		static constexpr bool is_losslessly_convertible_to_native =
-			integer_limits<T>::min >= (-9223372036854775807LL - 1LL) && integer_limits<T>::max <= 9223372036854775807LL;
+			integer_limits<underlying_type<T>>::min >= (-9223372036854775807LL - 1LL)
+			&& integer_limits<underlying_type<T>>::max <= 9223372036854775807LL;
 		static constexpr bool can_represent_native =
-			integer_limits<T>::min <= (-9223372036854775807LL - 1LL) && integer_limits<T>::max >= 9223372036854775807LL;
+			integer_limits<underlying_type<T>>::min <= (-9223372036854775807LL - 1LL)
+			&& integer_limits<underlying_type<T>>::max >= 9223372036854775807LL;
 	};
 	template <typename T, bool S = integer_traits_base<T>::is_signed>
 	struct integer_traits : signed_integer_traits<T>

include/toml++/impl/value.hpp

@@ -59,7 +59,7 @@ TOML_DISABLE_ARITHMETIC_WARNINGS;
 	TOML_SA_LIST_END																						\
 																											\
 	TOML_SA_LIST_NXT "A non-view type capable of (reasonably) representing a native TOML value type"		\
-	TOML_SA_LIST_BEG "any other integer type"																\
+	TOML_SA_LIST_BEG "any other integral type"																\
 	TOML_SA_LIST_SEP "any floating-point type"																\
 	TOML_SA_LIST_END																						\
 																											\
@@ -1221,7 +1221,7 @@ TOML_NAMESPACE_START
 				TOML_SA_LIST_END
 
 				TOML_SA_LIST_NXT "A non-view type capable of (reasonably) representing a native TOML value type"
-				TOML_SA_LIST_BEG "any other integer type"
+				TOML_SA_LIST_BEG "any other integral type"
 				TOML_SA_LIST_SEP "any floating-point type"
 				TOML_SA_LIST_END
 

tests/user_feedback.cpp

@@ -393,4 +393,23 @@ b = []
 			y = 2
 		)"sv);
 	}
+
+	SECTION("tomlplusplus/issues/207") // https://github.com/marzer/tomlplusplus/issues/207
+	{
+		enum class an_enum
+		{
+			zero,
+			one,
+			two,
+			three
+		};
+
+		parsing_should_succeed(FILE_LINE_ARGS,
+							   "val = 2\n",
+							   [](auto&& tbl)
+							   {
+								   const auto val = tbl["val"].template value_or<an_enum>(an_enum::zero);
+								   CHECK(val == an_enum::two);
+							   });
+	}
 }

toml.hpp

@@ -1742,10 +1742,22 @@ TOML_IMPL_NAMESPACE_START
 	template <typename T, typename... U>
 	inline constexpr bool first_is_same<T, T, U...> = true;
 
+	template <typename T, bool = std::is_enum_v<T>>
+	struct underlying_type_
+	{
+		using type = std::underlying_type_t<T>;
+	};
+	template <typename T>
+	struct underlying_type_<T, false>
+	{
+		using type = T;
+	};
+	template <typename T>
+	using underlying_type = typename underlying_type_<T>::type;
+
 	// general value traits
 	// (as they relate to their equivalent native TOML type)
-	template <typename T>
+	struct default_value_traits
-	struct value_traits
 	{
 		using native_type										  = void;
 		static constexpr bool is_native							  = false;
@@ -1755,6 +1767,27 @@ TOML_IMPL_NAMESPACE_START
 		static constexpr auto type								  = node_type::none;
 	};
 
+	template <typename T>
+	struct value_traits;
+
+	template <typename T, bool = std::is_enum_v<T>>
+	struct value_traits_base_selector
+	{
+		static_assert(!is_cvref<T>);
+
+		using type = default_value_traits;
+	};
+	template <typename T>
+	struct value_traits_base_selector<T, true>
+	{
+		static_assert(!is_cvref<T>);
+
+		using type = value_traits<underlying_type<T>>;
+	};
+
+	template <typename T>
+	struct value_traits : value_traits_base_selector<T>::type
+	{};
 	template <typename T>
 	struct value_traits<const T> : value_traits<T>
 	{};
@@ -1775,22 +1808,23 @@ TOML_IMPL_NAMESPACE_START
 	template <typename T>
 	struct integer_limits
 	{
-		static constexpr auto min = (std::numeric_limits<T>::min)();
+		static constexpr T min = T{ (std::numeric_limits<underlying_type<T>>::min)() };
-		static constexpr auto max = (std::numeric_limits<T>::max)();
+		static constexpr T max = T{ (std::numeric_limits<underlying_type<T>>::max)() };
 	};
 	template <typename T>
 	struct integer_traits_base : integer_limits<T>
 	{
 		using native_type				= int64_t;
-		static constexpr bool is_native = std::is_same_v<T, native_type>;
+		static constexpr bool is_native = std::is_same_v<underlying_type<T>, native_type>;
-		static constexpr bool is_signed = static_cast<T>(-1) < T{}; // for impls not specializing std::is_signed<T>
+		static constexpr bool is_signed = static_cast<underlying_type<T>>(-1) < underlying_type<T>{};
 		static constexpr auto type		= node_type::integer;
 		static constexpr bool can_partially_represent_native = true;
 	};
 	template <typename T>
 	struct unsigned_integer_traits : integer_traits_base<T>
 	{
-		static constexpr bool is_losslessly_convertible_to_native = integer_limits<T>::max <= 9223372036854775807ULL;
+		static constexpr bool is_losslessly_convertible_to_native =
+			integer_limits<underlying_type<T>>::max <= 9223372036854775807ULL;
 		static constexpr bool can_represent_native = false;
 	};
 	template <typename T>
@@ -1798,9 +1832,11 @@ TOML_IMPL_NAMESPACE_START
 	{
 		using native_type = int64_t;
 		static constexpr bool is_losslessly_convertible_to_native =
-			integer_limits<T>::min >= (-9223372036854775807LL - 1LL) && integer_limits<T>::max <= 9223372036854775807LL;
+			integer_limits<underlying_type<T>>::min >= (-9223372036854775807LL - 1LL)
+			&& integer_limits<underlying_type<T>>::max <= 9223372036854775807LL;
 		static constexpr bool can_represent_native =
-			integer_limits<T>::min <= (-9223372036854775807LL - 1LL) && integer_limits<T>::max >= 9223372036854775807LL;
+			integer_limits<underlying_type<T>>::min <= (-9223372036854775807LL - 1LL)
+			&& integer_limits<underlying_type<T>>::max >= 9223372036854775807LL;
 	};
 	template <typename T, bool S = integer_traits_base<T>::is_signed>
 	struct integer_traits : signed_integer_traits<T>
@@ -4765,7 +4801,7 @@ TOML_DISABLE_ARITHMETIC_WARNINGS;
 	TOML_SA_LIST_END																						\
 																											\
 	TOML_SA_LIST_NXT "A non-view type capable of (reasonably) representing a native TOML value type"		\
-	TOML_SA_LIST_BEG "any other integer type"																\
+	TOML_SA_LIST_BEG "any other integral type"																\
 	TOML_SA_LIST_SEP "any floating-point type"																\
 	TOML_SA_LIST_END																						\
 																											\
@@ -5743,7 +5779,7 @@ TOML_NAMESPACE_START
 				TOML_SA_LIST_END
 
 				TOML_SA_LIST_NXT "A non-view type capable of (reasonably) representing a native TOML value type"
-				TOML_SA_LIST_BEG "any other integer type"
+				TOML_SA_LIST_BEG "any other integral type"
 				TOML_SA_LIST_SEP "any floating-point type"
 				TOML_SA_LIST_END