include/meta/meta_fwd.hpp

0001 /// \file meta_fwd.hpp Forward declarations
0002 //
0003 // Meta library
0004 //
0005 //  Copyright Eric Niebler 2014-present
0006 //
0007 //  Use, modification and distribution is subject to the
0008 //  Boost Software License, Version 1.0. (See accompanying
0009 //  file LICENSE_1_0.txt or copy at
0010 //  http://www.boost.org/LICENSE_1_0.txt)
0011 //
0012 // Project home: https://github.com/ericniebler/meta
0013 //
0014
0015 #ifndef META_FWD_HPP
0016 #define META_FWD_HPP
0017
0018 #include <type_traits>
0019 #include <utility>
0020
0021 #ifdef __clang__
0022 #pragma GCC diagnostic push
0023 #pragma GCC diagnostic ignored "-Wmissing-variable-declarations"
0024 #endif
0025
0026 #define META_CXX_STD_14 201402L
0027 #define META_CXX_STD_17 201703L
0028
0029 #if defined(_MSVC_LANG) && _MSVC_LANG > __cplusplus // Older clangs define _MSVC_LANG < __cplusplus
0030 #define META_CXX_VER _MSVC_LANG
0031 #else
0032 #define META_CXX_VER __cplusplus
0033 #endif
0034
0035 #if defined(__apple_build_version__) || defined(__clang__)
0036 #if defined(__apple_build_version__) || (defined(__clang__) && __clang_major__ < 6)
0037 #define META_WORKAROUND_LLVM_28385 // https://llvm.org/bugs/show_bug.cgi?id=28385
0038 #endif
0039
0040 #elif defined(_MSC_VER)
0041 #define META_HAS_MAKE_INTEGER_SEQ 1
0042 #if _MSC_VER < 1920
0043 #define META_WORKAROUND_MSVC_702792 // Bogus C4018 comparing constant expressions with dependent type
0044 #define META_WORKAROUND_MSVC_703656 // ICE with pack expansion inside decltype in alias template
0045 #endif
0046
0047 #if _MSC_VER < 1921
0048 #define META_WORKAROUND_MSVC_756112 // fold expression + alias templates in template argument
0049 #endif
0050
0051 #elif defined(__GNUC__)
0052 #define META_WORKAROUND_GCC_86356 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86356
0053 #if __GNUC__ < 8
0054 #define META_WORKAROUND_GCC_UNKNOWN1 // Older GCCs don't like fold + debug + -march=native
0055 #endif
0056 #if __GNUC__ == 5 && __GNUC_MINOR__ == 1
0057 #define META_WORKAROUND_GCC_66405 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66405
0058 #endif
0059 #if __GNUC__ < 5
0060 #define META_WORKAROUND_CWG_1558 // https://wg21.link/cwg1558
0061 #endif
0062 #endif
0063
0064 #ifndef META_CXX_VARIABLE_TEMPLATES
0065 #ifdef __cpp_variable_templates
0066 #define META_CXX_VARIABLE_TEMPLATES __cpp_variable_templates
0067 #else
0068 #define META_CXX_VARIABLE_TEMPLATES (META_CXX_VER >= META_CXX_STD_14)
0069 #endif
0070 #endif
0071
0072 #ifndef META_CXX_INLINE_VARIABLES
0073 #ifdef __cpp_inline_variables
0074 #define META_CXX_INLINE_VARIABLES __cpp_inline_variables
0075 #else
0076 #define META_CXX_INLINE_VARIABLES (META_CXX_VER >= META_CXX_STD_17)
0077 #endif
0078 #endif
0079
0080 #ifndef META_INLINE_VAR
0081 #if META_CXX_INLINE_VARIABLES
0082 #define META_INLINE_VAR inline
0083 #else
0084 #define META_INLINE_VAR
0085 #endif
0086 #endif
0087
0088 #ifndef META_CXX_INTEGER_SEQUENCE
0089 #ifdef __cpp_lib_integer_sequence
0090 #define META_CXX_INTEGER_SEQUENCE __cpp_lib_integer_sequence
0091 #else
0092 #define META_CXX_INTEGER_SEQUENCE (META_CXX_VER >= META_CXX_STD_14)
0093 #endif
0094 #endif
0095
0096 #ifndef META_HAS_MAKE_INTEGER_SEQ
0097 #ifdef __has_builtin
0098 #if __has_builtin(__make_integer_seq)
0099 #define META_HAS_MAKE_INTEGER_SEQ 1
0100 #endif
0101 #endif
0102 #endif
0103 #ifndef META_HAS_MAKE_INTEGER_SEQ
0104 #define META_HAS_MAKE_INTEGER_SEQ 0
0105 #endif
0106
0107 #ifndef META_HAS_TYPE_PACK_ELEMENT
0108 #ifdef __has_builtin
0109 #if __has_builtin(__type_pack_element)
0110 #define META_HAS_TYPE_PACK_ELEMENT 1
0111 #endif
0112 #endif
0113 #endif
0114 #ifndef META_HAS_TYPE_PACK_ELEMENT
0115 #define META_HAS_TYPE_PACK_ELEMENT 0
0116 #endif
0117
0118 #if !defined(META_DEPRECATED) && !defined(META_DISABLE_DEPRECATED_WARNINGS)
0119 #if defined(__cpp_attribute_deprecated) || META_CXX_VER >= META_CXX_STD_14
0120 #define META_DEPRECATED(...) [[deprecated(__VA_ARGS__)]]
0121 #elif defined(__clang__) || defined(__GNUC__)
0122 #define META_DEPRECATED(...) __attribute__((deprecated(__VA_ARGS__)))
0123 #endif
0124 #endif
0125 #ifndef META_DEPRECATED
0126 #define META_DEPRECATED(...)
0127 #endif
0128
0129 #ifndef META_CXX_FOLD_EXPRESSIONS
0130 #ifdef __cpp_fold_expressions
0131 #define META_CXX_FOLD_EXPRESSIONS __cpp_fold_expressions
0132 #else
0133 #define META_CXX_FOLD_EXPRESSIONS (META_CXX_VER >= META_CXX_STD_17)
0134 #endif
0135 #endif
0136
0137 #if META_CXX_FOLD_EXPRESSIONS
0138 #if !META_CXX_VARIABLE_TEMPLATES
0139 #error Fold expressions, but no variable templates?
0140 #endif
0141 #endif
0142
0143 #if (defined(__cpp_concepts) && __cpp_concepts > 0) || defined(META_DOXYGEN_INVOKED)
0144 #if !META_CXX_VARIABLE_TEMPLATES
0145 #error Concepts, but no variable templates?
0146 #endif
0147 #if __cpp_concepts <= 201507L && !defined(META_DOXYGEN_INVOKED)
0148 #define META_CONCEPT concept bool
0149 // TS concepts subsumption barrier for atomic expressions
0150 #define META_CONCEPT_BARRIER(...) ::meta::detail::barrier<__VA_ARGS__>
0151 #define META_TYPE_CONSTRAINT(...) typename
0152 #else
0153 #define META_CONCEPT concept
0154 #define META_CONCEPT_BARRIER(...) __VA_ARGS__
0155 #define META_TYPE_CONSTRAINT(...) __VA_ARGS__
0156 #endif
0157 #else
0158 #define META_TYPE_CONSTRAINT(...) typename
0159 #endif
0160
0161 #if (defined(__cpp_lib_type_trait_variable_templates) && \
0162     __cpp_lib_type_trait_variable_templates > 0)
0163 #define META_CXX_TRAIT_VARIABLE_TEMPLATES 1
0164 #else
0165 #define META_CXX_TRAIT_VARIABLE_TEMPLATES 0
0166 #endif
0167
0168 #if defined(__clang__)
0169 #define META_IS_SAME(...) __is_same(__VA_ARGS__)
0170 #elif defined(__GNUC__) && __GNUC__ >= 6
0171 #define META_IS_SAME(...) __is_same_as(__VA_ARGS__)
0172 #elif META_CXX_TRAIT_VARIABLE_TEMPLATES
0173 #define META_IS_SAME(...) std::is_same_v<__VA_ARGS__>
0174 #else
0175 #define META_IS_SAME(...) std::is_same<__VA_ARGS__>::value
0176 #endif
0177
0178 #if defined(__GNUC__) || defined(_MSC_VER)
0179 #define META_IS_BASE_OF(...) __is_base_of(__VA_ARGS__)
0180 #elif META_CXX_TRAIT_VARIABLE_TEMPLATES
0181 #define META_IS_BASE_OF(...) std::is_base_of_v<__VA_ARGS__>
0182 #else
0183 #define META_IS_BASE_OF(...) std::is_base_of<__VA_ARGS__>::value
0184 #endif
0185
0186 #if defined(__clang__) || defined(_MSC_VER) || \
0187     (defined(__GNUC__) && __GNUC__ >= 8)
0188 #define META_IS_CONSTRUCTIBLE(...) __is_constructible(__VA_ARGS__)
0189 #elif META_CXX_TRAIT_VARIABLE_TEMPLATES
0190 #define META_IS_CONSTRUCTIBLE(...) std::is_constructible_v<__VA_ARGS__>
0191 #else
0192 #define META_IS_CONSTRUCTIBLE(...) std::is_constructible<__VA_ARGS__>::value
0193 #endif
0194
0195 /// \cond
0196 // Non-portable forward declarations of standard containers
0197 #ifdef _LIBCPP_VERSION
0198 #define META_BEGIN_NAMESPACE_STD _LIBCPP_BEGIN_NAMESPACE_STD
0199 #define META_END_NAMESPACE_STD _LIBCPP_END_NAMESPACE_STD
0200 #elif defined(_MSVC_STL_VERSION)
0201 #define META_BEGIN_NAMESPACE_STD _STD_BEGIN
0202 #define META_END_NAMESPACE_STD _STD_END
0203 #else
0204 #define META_BEGIN_NAMESPACE_STD namespace std {
0205 #define META_END_NAMESPACE_STD }
0206 #endif
0207
0208 #if defined(__GLIBCXX__)
0209 #define META_BEGIN_NAMESPACE_VERSION _GLIBCXX_BEGIN_NAMESPACE_VERSION
0210 #define META_END_NAMESPACE_VERSION _GLIBCXX_END_NAMESPACE_VERSION
0211 #define META_BEGIN_NAMESPACE_CONTAINER _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
0212 #define META_END_NAMESPACE_CONTAINER _GLIBCXX_END_NAMESPACE_CONTAINER
0213 #else
0214 #define META_BEGIN_NAMESPACE_VERSION
0215 #define META_END_NAMESPACE_VERSION
0216 #define META_BEGIN_NAMESPACE_CONTAINER
0217 #define META_END_NAMESPACE_CONTAINER
0218 #endif
0219
0220 #if defined(_LIBCPP_VERSION) && _LIBCPP_VERSION >= 4000
0221 #define META_TEMPLATE_VIS _LIBCPP_TEMPLATE_VIS
0222 #elif defined(_LIBCPP_VERSION)
0223 #define META_TEMPLATE_VIS _LIBCPP_TYPE_VIS_ONLY
0224 #else
0225 #define META_TEMPLATE_VIS
0226 #endif
0227 /// \endcond
0228
0229 namespace meta
0230 {
0231 #if META_CXX_INTEGER_SEQUENCE
0232     using std::integer_sequence;
0233 #else
0234     template <typename T, T...>
0235     struct integer_sequence;
0236 #endif
0237
0238     template <typename... Ts>
0239     struct list;
0240
0241     template <typename T>
0242     struct id;
0243
0244     template <template <typename...> class>
0245     struct quote;
0246
0247     template <typename T, template <T...> class F>
0248     struct quote_i;
0249
0250     template <template <typename...> class C, typename... Ts>
0251     struct defer;
0252
0253     template <typename T, template <T...> class C, T... Is>
0254     struct defer_i;
0255
0256 #if META_CXX_VARIABLE_TEMPLATES || defined(META_DOXYGEN_INVOKED)
0257     /// is_v
0258     /// Test whether a type \p T is an instantiation of class
0259     /// template \p C.
0260     /// \ingroup trait
0261     template <typename, template <typename...> class>
0262     META_INLINE_VAR constexpr bool is_v = false;
0263     template <typename... Ts, template <typename...> class C>
0264     META_INLINE_VAR constexpr bool is_v<C<Ts...>, C> = true;
0265 #endif
0266
0267 #ifdef META_CONCEPT
0268     namespace detail
0269     {
0270         template <bool B>
0271         META_INLINE_VAR constexpr bool barrier = B;
0272
0273         template <class T, T> struct require_constant; // not defined
0274     }
0275
0276     template <typename...>
0277     META_CONCEPT is_true = META_CONCEPT_BARRIER(true);
0278
0279     template <typename T, typename U>
0280     META_CONCEPT same_as =
0281         META_CONCEPT_BARRIER(META_IS_SAME(T, U));
0282
0283     template <template <typename...> class C, typename... Ts>
0284     META_CONCEPT valid = requires
0285     {
0286         typename C<Ts...>;
0287     };
0288
0289     template <typename T, template <T...> class C, T... Is>
0290     META_CONCEPT valid_i = requires
0291     {
0292         typename C<Is...>;
0293     };
0294
0295     template <typename T>
0296     META_CONCEPT trait = requires
0297     {
0298         typename T::type;
0299     };
0300
0301     template <typename T>
0302     META_CONCEPT invocable = requires
0303     {
0304         typename quote<T::template invoke>;
0305     };
0306
0307     template <typename T>
0308     META_CONCEPT list_like = is_v<T, list>;
0309
0310     // clang-format off
0311     template <typename T>
0312     META_CONCEPT integral = requires
0313     {
0314         typename T::type;
0315         typename T::value_type;
0316         typename T::type::value_type;
0317     }
0318     && same_as<typename T::value_type, typename T::type::value_type>
0319 #if META_CXX_TRAIT_VARIABLE_TEMPLATES
0320     && std::is_integral_v<typename T::value_type>
0321 #else
0322     && std::is_integral<typename T::value_type>::value
0323 #endif
0324
0325     && requires
0326     {
0327         // { T::value } -> same_as<const typename T::value_type&>;
0328         T::value;
0329         requires same_as<decltype(T::value), const typename T::value_type>;
0330         typename detail::require_constant<decltype(T::value), T::value>;
0331
0332         // { T::type::value } -> same_as<const typename T::value_type&>;
0333         T::type::value;
0334         requires same_as<decltype(T::type::value), const typename T::value_type>;
0335         typename detail::require_constant<decltype(T::type::value), T::type::value>;
0336         requires T::value == T::type::value;
0337
0338         // { T{}() } -> same_as<typename T::value_type>;
0339         T{}();
0340         requires same_as<decltype(T{}()), typename T::value_type>;
0341         typename detail::require_constant<decltype(T{}()), T{}()>;
0342         requires T{}() == T::value;
0343
0344         // { T{} } -> typename T::value_type;
0345     };
0346     // clang-format on
0347 #endif // META_CONCEPT
0348
0349     namespace extension
0350     {
0351         template <META_TYPE_CONSTRAINT(invocable) F, typename L>
0352         struct apply;
0353     }
0354 } // namespace meta
0355
0356 #ifdef __clang__
0357 #pragma GCC diagnostic pop
0358 #endif
0359
0360 #endif