From 7b2d59162df376aa21d6d18a4c9a480e3919e946 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Th=C3=A9o=20Delrieu?= Date: Fri, 17 Sep 2021 17:06:11 +0200 Subject: [PATCH] meta: fix is_compatible/constructible traits The previous version relied on the existence of an 'iterator' type. As mentioned in comments, this is not the proper way to do it and causes issues with certain types (e.g. views from range-v3). Add a 'is_range' trait that properly detects the return type of 'begin'/'end', and use it in instead. --- include/nlohmann/detail/macro_scope.hpp | 42 ++- include/nlohmann/detail/macro_unscope.hpp | 1 + .../nlohmann/detail/meta/call_std/begin.hpp | 8 + include/nlohmann/detail/meta/call_std/end.hpp | 8 + include/nlohmann/detail/meta/type_traits.hpp | 76 +++-- single_include/nlohmann/json.hpp | 272 ++++++++++++------ test/src/unit-udt.cpp | 30 ++ 7 files changed, 313 insertions(+), 124 deletions(-) create mode 100644 include/nlohmann/detail/meta/call_std/begin.hpp create mode 100644 include/nlohmann/detail/meta/call_std/end.hpp diff --git a/include/nlohmann/detail/macro_scope.hpp b/include/nlohmann/detail/macro_scope.hpp index 76a0dc62cf..c2a65bdda6 100644 --- a/include/nlohmann/detail/macro_scope.hpp +++ b/include/nlohmann/detail/macro_scope.hpp @@ -1,7 +1,8 @@ #pragma once -#include // pair +#include // declval, pair #include +#include // This file contains all internal macro definitions // You MUST include macro_unscope.hpp at the end of json.hpp to undef all of them @@ -292,6 +293,45 @@ inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \ inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) } + +// inspired from https://stackoverflow.com/a/26745591 +// allows to call any std function as if (e.g. with begin): +// using std::begin; begin(x); +// +// it allows using the detected idiom to retrieve the return type +// of such an expression +#define NLOHMANN_CAN_CALL_STD_FUNC_IMPL(std_name) \ + namespace detail { \ + using std::std_name; \ + \ + template \ + using result_of_##std_name = decltype(std_name(std::declval()...)); \ + } \ + \ + namespace detail2 { \ + struct std_name##_tag \ + { \ + }; \ + \ + template \ + std_name##_tag std_name(T&&...); \ + \ + template \ + using result_of_##std_name = decltype(std_name(std::declval()...)); \ + \ + template \ + struct would_call_std_##std_name \ + { \ + static constexpr auto const value = ::nlohmann::detail:: \ + is_detected_exact::value; \ + }; \ + } /* namespace detail2 */ \ + \ + template \ + struct would_call_std_##std_name : detail2::would_call_std_##std_name \ + { \ + } + #ifndef JSON_USE_IMPLICIT_CONVERSIONS #define JSON_USE_IMPLICIT_CONVERSIONS 1 #endif diff --git a/include/nlohmann/detail/macro_unscope.hpp b/include/nlohmann/detail/macro_unscope.hpp index 3f56e4b85e..67bf1466bc 100644 --- a/include/nlohmann/detail/macro_unscope.hpp +++ b/include/nlohmann/detail/macro_unscope.hpp @@ -19,5 +19,6 @@ #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION #undef NLOHMANN_BASIC_JSON_TPL #undef JSON_EXPLICIT +#undef NLOHMANN_CAN_CALL_STD_FUNC_IMPL #include diff --git a/include/nlohmann/detail/meta/call_std/begin.hpp b/include/nlohmann/detail/meta/call_std/begin.hpp new file mode 100644 index 0000000000..da937144c8 --- /dev/null +++ b/include/nlohmann/detail/meta/call_std/begin.hpp @@ -0,0 +1,8 @@ +#pragma once + +#include + +namespace nlohmann +{ +NLOHMANN_CAN_CALL_STD_FUNC_IMPL(begin); +} // namespace nlohmann diff --git a/include/nlohmann/detail/meta/call_std/end.hpp b/include/nlohmann/detail/meta/call_std/end.hpp new file mode 100644 index 0000000000..1909007398 --- /dev/null +++ b/include/nlohmann/detail/meta/call_std/end.hpp @@ -0,0 +1,8 @@ +#pragma once + +#include + +namespace nlohmann +{ +NLOHMANN_CAN_CALL_STD_FUNC_IMPL(end); +} // namespace nlohmann diff --git a/include/nlohmann/detail/meta/type_traits.hpp b/include/nlohmann/detail/meta/type_traits.hpp index ede55acc26..ca6051e7cd 100644 --- a/include/nlohmann/detail/meta/type_traits.hpp +++ b/include/nlohmann/detail/meta/type_traits.hpp @@ -5,8 +5,11 @@ #include // declval #include // tuple -#include #include + +#include +#include +#include #include #include #include @@ -79,9 +82,6 @@ using reference_t = typename T::reference; template using iterator_category_t = typename T::iterator_category; -template -using iterator_t = typename T::iterator; - template using to_json_function = decltype(T::to_json(std::declval()...)); @@ -217,6 +217,31 @@ struct is_iterator_traits> is_detected::value; }; +template +struct is_range +{ + private: + using t_ref = typename std::add_lvalue_reference::type; + + using iterator = detected_t; + using sentinel = detected_t; + + // to be 100% correct, it should use https://en.cppreference.com/w/cpp/iterator/input_or_output_iterator + // and https://en.cppreference.com/w/cpp/iterator/sentinel_for + // but reimplementing these would be too much work, as a lot of other concepts are used underneath + static constexpr auto is_iterator_begin = + is_iterator_traits>::value; + + public: + static constexpr bool value = !std::is_same::value && !std::is_same::value && is_iterator_begin; +}; + +template +using iterator_t = enable_if_t::value, result_of_begin())>>; + +template +using range_value_t = value_type_t>>; + // The following implementation of is_complete_type is taken from // https://blogs.msdn.microsoft.com/vcblog/2015/12/02/partial-support-for-expression-sfinae-in-vs-2015-update-1/ // and is written by Xiang Fan who agreed to using it in this library. @@ -291,8 +316,9 @@ struct is_compatible_string_type_impl : std::false_type {}; template struct is_compatible_string_type_impl < BasicJsonType, CompatibleStringType, - enable_if_t::value >> + enable_if_t::value >> { static constexpr auto value = is_constructible::value; @@ -327,17 +353,13 @@ struct is_compatible_array_type_impl : std::false_type {}; template struct is_compatible_array_type_impl < BasicJsonType, CompatibleArrayType, - enable_if_t < is_detected::value&& + enable_if_t < is_detected::value&& -// This is needed because json_reverse_iterator has a ::iterator type... -// Therefore it is detected as a CompatibleArrayType. -// The real fix would be to have an Iterable concept. - !is_iterator_traits < - iterator_traits>::value >> + is_iterator_traits>>::value >> { static constexpr bool value = is_constructible::value; + range_value_t>::value; }; template @@ -359,28 +381,26 @@ struct is_constructible_array_type_impl < BasicJsonType, ConstructibleArrayType, enable_if_t < !std::is_same::value&& + !is_compatible_string_type::value&& is_default_constructible::value&& (std::is_move_assignable::value || std::is_copy_assignable::value)&& -is_detected::value&& is_detected::value&& +is_iterator_traits>>::value&& +is_detected::value&& is_complete_type < -detected_t>::value >> +detected_t>::value >> { + using value_type = range_value_t; + static constexpr bool value = - // This is needed because json_reverse_iterator has a ::iterator type, - // furthermore, std::back_insert_iterator (and other iterators) have a - // base class `iterator`... Therefore it is detected as a - // ConstructibleArrayType. The real fix would be to have an Iterable - // concept. - !is_iterator_traits>::value && - - (std::is_same::value || - has_from_json::value || - has_non_default_from_json < - BasicJsonType, typename ConstructibleArrayType::value_type >::value); + std::is_same::value || + has_from_json::value || + has_non_default_from_json < + BasicJsonType, + value_type >::value; }; template diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp index 9c27aabbe5..7d2e59e19c 100644 --- a/single_include/nlohmann/json.hpp +++ b/single_include/nlohmann/json.hpp @@ -167,7 +167,7 @@ inline bool operator<(const value_t lhs, const value_t rhs) noexcept // #include -#include // pair +#include // declval, pair // #include @@ -2214,6 +2214,83 @@ JSON_HEDLEY_DIAGNOSTIC_POP #endif /* !defined(JSON_HEDLEY_VERSION) || (JSON_HEDLEY_VERSION < X) */ +// #include + + +#include + +// #include + + +namespace nlohmann +{ +namespace detail +{ +template struct make_void +{ + using type = void; +}; +template using void_t = typename make_void::type; +} // namespace detail +} // namespace nlohmann + + +// https://en.cppreference.com/w/cpp/experimental/is_detected +namespace nlohmann +{ +namespace detail +{ +struct nonesuch +{ + nonesuch() = delete; + ~nonesuch() = delete; + nonesuch(nonesuch const&) = delete; + nonesuch(nonesuch const&&) = delete; + void operator=(nonesuch const&) = delete; + void operator=(nonesuch&&) = delete; +}; + +template class Op, + class... Args> +struct detector +{ + using value_t = std::false_type; + using type = Default; +}; + +template class Op, class... Args> +struct detector>, Op, Args...> +{ + using value_t = std::true_type; + using type = Op; +}; + +template class Op, class... Args> +using is_detected = typename detector::value_t; + +template class Op, class... Args> +struct is_detected_lazy : is_detected { }; + +template class Op, class... Args> +using detected_t = typename detector::type; + +template class Op, class... Args> +using detected_or = detector; + +template class Op, class... Args> +using detected_or_t = typename detected_or::type; + +template class Op, class... Args> +using is_detected_exact = std::is_same>; + +template class Op, class... Args> +using is_detected_convertible = + std::is_convertible, To>; +} // namespace detail +} // namespace nlohmann + // This file contains all internal macro definitions // You MUST include macro_unscope.hpp at the end of json.hpp to undef all of them @@ -2504,6 +2581,45 @@ JSON_HEDLEY_DIAGNOSTIC_POP inline void to_json(nlohmann::json& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) } \ inline void from_json(const nlohmann::json& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) } + +// inspired from https://stackoverflow.com/a/26745591 +// allows to call any std function as if (e.g. with begin): +// using std::begin; begin(x); +// +// it allows using the detected idiom to retrieve the return type +// of such an expression +#define NLOHMANN_CAN_CALL_STD_FUNC_IMPL(std_name) \ + namespace detail { \ + using std::std_name; \ + \ + template \ + using result_of_##std_name = decltype(std_name(std::declval()...)); \ + } \ + \ + namespace detail2 { \ + struct std_name##_tag \ + { \ + }; \ + \ + template \ + std_name##_tag std_name(T&&...); \ + \ + template \ + using result_of_##std_name = decltype(std_name(std::declval()...)); \ + \ + template \ + struct would_call_std_##std_name \ + { \ + static constexpr auto const value = ::nlohmann::detail:: \ + is_detected_exact::value; \ + }; \ + } /* namespace detail2 */ \ + \ + template \ + struct would_call_std_##std_name : detail2::would_call_std_##std_name \ + { \ + } + #ifndef JSON_USE_IMPLICIT_CONVERSIONS #define JSON_USE_IMPLICIT_CONVERSIONS 1 #endif @@ -3207,6 +3323,9 @@ template struct identity_tag {}; #include // declval #include // tuple +// #include + + // #include @@ -3214,19 +3333,6 @@ template struct identity_tag {}; // #include - -namespace nlohmann -{ -namespace detail -{ -template struct make_void -{ - using type = void; -}; -template using void_t = typename make_void::type; -} // namespace detail -} // namespace nlohmann - // #include @@ -3275,73 +3381,31 @@ struct iterator_traits::value>> } // namespace detail } // namespace nlohmann -// #include +// #include -// #include -// #include - - -#include - -// #include +// #include -// https://en.cppreference.com/w/cpp/experimental/is_detected namespace nlohmann { -namespace detail -{ -struct nonesuch -{ - nonesuch() = delete; - ~nonesuch() = delete; - nonesuch(nonesuch const&) = delete; - nonesuch(nonesuch const&&) = delete; - void operator=(nonesuch const&) = delete; - void operator=(nonesuch&&) = delete; -}; - -template class Op, - class... Args> -struct detector -{ - using value_t = std::false_type; - using type = Default; -}; - -template class Op, class... Args> -struct detector>, Op, Args...> -{ - using value_t = std::true_type; - using type = Op; -}; +NLOHMANN_CAN_CALL_STD_FUNC_IMPL(begin); +} // namespace nlohmann -template class Op, class... Args> -using is_detected = typename detector::value_t; +// #include -template class Op, class... Args> -struct is_detected_lazy : is_detected { }; -template class Op, class... Args> -using detected_t = typename detector::type; +// #include -template class Op, class... Args> -using detected_or = detector; -template class Op, class... Args> -using detected_or_t = typename detected_or::type; +namespace nlohmann +{ +NLOHMANN_CAN_CALL_STD_FUNC_IMPL(end); +} // namespace nlohmann -template class Op, class... Args> -using is_detected_exact = std::is_same>; +// #include -template class Op, class... Args> -using is_detected_convertible = - std::is_convertible, To>; -} // namespace detail -} // namespace nlohmann +// #include // #include #ifndef INCLUDE_NLOHMANN_JSON_FWD_HPP_ @@ -3492,9 +3556,6 @@ using reference_t = typename T::reference; template using iterator_category_t = typename T::iterator_category; -template -using iterator_t = typename T::iterator; - template using to_json_function = decltype(T::to_json(std::declval()...)); @@ -3630,6 +3691,31 @@ struct is_iterator_traits> is_detected::value; }; +template +struct is_range +{ + private: + using t_ref = typename std::add_lvalue_reference::type; + + using iterator = detected_t; + using sentinel = detected_t; + + // to be 100% correct, it should use https://en.cppreference.com/w/cpp/iterator/input_or_output_iterator + // and https://en.cppreference.com/w/cpp/iterator/sentinel_for + // but reimplementing these would be too much work, as a lot of other concepts are used underneath + static constexpr auto is_iterator_begin = + is_iterator_traits>::value; + + public: + static constexpr bool value = !std::is_same::value && !std::is_same::value && is_iterator_begin; +}; + +template +using iterator_t = enable_if_t::value, result_of_begin())>>; + +template +using range_value_t = value_type_t>>; + // The following implementation of is_complete_type is taken from // https://blogs.msdn.microsoft.com/vcblog/2015/12/02/partial-support-for-expression-sfinae-in-vs-2015-update-1/ // and is written by Xiang Fan who agreed to using it in this library. @@ -3704,8 +3790,9 @@ struct is_compatible_string_type_impl : std::false_type {}; template struct is_compatible_string_type_impl < BasicJsonType, CompatibleStringType, - enable_if_t::value >> + enable_if_t::value >> { static constexpr auto value = is_constructible::value; @@ -3740,17 +3827,13 @@ struct is_compatible_array_type_impl : std::false_type {}; template struct is_compatible_array_type_impl < BasicJsonType, CompatibleArrayType, - enable_if_t < is_detected::value&& + enable_if_t < is_detected::value&& -// This is needed because json_reverse_iterator has a ::iterator type... -// Therefore it is detected as a CompatibleArrayType. -// The real fix would be to have an Iterable concept. - !is_iterator_traits < - iterator_traits>::value >> + is_iterator_traits>>::value >> { static constexpr bool value = is_constructible::value; + range_value_t>::value; }; template @@ -3772,28 +3855,26 @@ struct is_constructible_array_type_impl < BasicJsonType, ConstructibleArrayType, enable_if_t < !std::is_same::value&& + !is_compatible_string_type::value&& is_default_constructible::value&& (std::is_move_assignable::value || std::is_copy_assignable::value)&& -is_detected::value&& is_detected::value&& +is_iterator_traits>>::value&& +is_detected::value&& is_complete_type < -detected_t>::value >> +detected_t>::value >> { + using value_type = range_value_t; + static constexpr bool value = - // This is needed because json_reverse_iterator has a ::iterator type, - // furthermore, std::back_insert_iterator (and other iterators) have a - // base class `iterator`... Therefore it is detected as a - // ConstructibleArrayType. The real fix would be to have an Iterable - // concept. - !is_iterator_traits>::value && - - (std::is_same::value || - has_from_json::value || - has_non_default_from_json < - BasicJsonType, typename ConstructibleArrayType::value_type >::value); + std::is_same::value || + has_from_json::value || + has_non_default_from_json < + BasicJsonType, + value_type >::value; }; template @@ -26489,6 +26570,7 @@ inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION #undef NLOHMANN_BASIC_JSON_TPL #undef JSON_EXPLICIT +#undef NLOHMANN_CAN_CALL_STD_FUNC_IMPL // #include diff --git a/test/src/unit-udt.cpp b/test/src/unit-udt.cpp index f83ef9a0ac..eed6c41325 100644 --- a/test/src/unit-udt.cpp +++ b/test/src/unit-udt.cpp @@ -850,4 +850,34 @@ TEST_CASE("Issue #1237") static_assert(!std::is_convertible::value, ""); } +namespace +{ +class no_iterator_type +{ + public: + no_iterator_type(std::initializer_list l) + : _v(l) + {} + + std::vector::const_iterator begin() const + { + return _v.begin(); + } + + std::vector::const_iterator end() const + { + return _v.end(); + } + + private: + std::vector _v; +}; +} // namespace + +TEST_CASE("compatible array type, without iterator type alias") +{ + no_iterator_type vec{1, 2, 3}; + json j = vec; +} + DOCTEST_GCC_SUPPRESS_WARNING_POP