diff options
Diffstat (limited to 'absl/meta/type_traits.h')
| -rw-r--r-- | absl/meta/type_traits.h | 109 |
1 files changed, 106 insertions, 3 deletions
diff --git a/absl/meta/type_traits.h b/absl/meta/type_traits.h index a8068e315ed3..c08e3754689b 100644 --- a/absl/meta/type_traits.h +++ b/absl/meta/type_traits.h @@ -43,8 +43,39 @@ namespace absl { +// Defined and documented later on in this file. +template <typename T> +struct is_trivially_move_assignable; + namespace type_traits_internal { +// Silence MSVC warnings about the destructor being defined as deleted. +#if defined(_MSC_VER) && !defined(__GNUC__) +#pragma warning(push) +#pragma warning(disable : 4624) +#endif // defined(_MSC_VER) && !defined(__GNUC__) + +template <class T> +union SingleMemberUnion { + T t; +}; + +// Restore the state of the destructor warning that was silenced above. +#if defined(_MSC_VER) && !defined(__GNUC__) +#pragma warning(pop) +#endif // defined(_MSC_VER) && !defined(__GNUC__) + +template <class T> +struct IsTriviallyMoveAssignableReference : std::false_type {}; + +template <class T> +struct IsTriviallyMoveAssignableReference<T&> + : absl::is_trivially_move_assignable<T>::type {}; + +template <class T> +struct IsTriviallyMoveAssignableReference<T&&> + : absl::is_trivially_move_assignable<T>::type {}; + template <typename... Ts> struct VoidTImpl { using type = void; @@ -275,6 +306,40 @@ struct is_trivially_default_constructible #endif // ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE }; +// is_trivially_move_constructible() +// +// Determines whether the passed type `T` is trivially move constructible. +// +// This metafunction is designed to be a drop-in replacement for the C++11 +// `std::is_trivially_move_constructible()` metafunction for platforms that have +// incomplete C++11 support (such as libstdc++ 4.x). On any platforms that do +// fully support C++11, we check whether this yields the same result as the std +// implementation. +// +// NOTE: `T obj(declval<T>());` needs to be well-formed and not call any +// nontrivial operation. Nontrivially destructible types will cause the +// expression to be nontrivial. +template <typename T> +struct is_trivially_move_constructible + : std::conditional< + std::is_object<T>::value && !std::is_array<T>::value, + std::is_move_constructible< + type_traits_internal::SingleMemberUnion<T>>, + std::is_reference<T>>::type::type { +#ifdef ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE + private: + static constexpr bool compliant = + std::is_trivially_move_constructible<T>::value == + is_trivially_move_constructible::value; + static_assert(compliant || std::is_trivially_move_constructible<T>::value, + "Not compliant with std::is_trivially_move_constructible; " + "Standard: false, Implementation: true"); + static_assert(compliant || !std::is_trivially_move_constructible<T>::value, + "Not compliant with std::is_trivially_move_constructible; " + "Standard: true, Implementation: false"); +#endif // ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE +}; + // is_trivially_copy_constructible() // // Determines whether the passed type `T` is trivially copy constructible. @@ -290,9 +355,11 @@ struct is_trivially_default_constructible // expression to be nontrivial. template <typename T> struct is_trivially_copy_constructible - : std::integral_constant<bool, __has_trivial_copy(T) && - std::is_copy_constructible<T>::value && - is_trivially_destructible<T>::value> { + : std::conditional< + std::is_object<T>::value && !std::is_array<T>::value, + std::is_copy_constructible< + type_traits_internal::SingleMemberUnion<T>>, + std::is_lvalue_reference<T>>::type::type { #ifdef ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE private: static constexpr bool compliant = @@ -307,6 +374,42 @@ struct is_trivially_copy_constructible #endif // ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE }; +// is_trivially_move_assignable() +// +// Determines whether the passed type `T` is trivially move assignable. +// +// This metafunction is designed to be a drop-in replacement for the C++11 +// `std::is_trivially_move_assignable()` metafunction for platforms that have +// incomplete C++11 support (such as libstdc++ 4.x). On any platforms that do +// fully support C++11, we check whether this yields the same result as the std +// implementation. +// +// NOTE: `is_assignable<T, U>::value` is `true` if the expression +// `declval<T>() = declval<U>()` is well-formed when treated as an unevaluated +// operand. `is_trivially_assignable<T, U>` requires the assignment to call no +// operation that is not trivial. `is_trivially_copy_assignable<T>` is simply +// `is_trivially_assignable<T&, T>`. +template <typename T> +struct is_trivially_move_assignable + : std::conditional< + std::is_object<T>::value && !std::is_array<T>::value, + std::is_move_assignable<type_traits_internal::SingleMemberUnion<T>>, + type_traits_internal::IsTriviallyMoveAssignableReference<T>>::type:: + type { +#ifdef ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE + private: + static constexpr bool compliant = + std::is_trivially_move_assignable<T>::value == + is_trivially_move_assignable::value; + static_assert(compliant || std::is_trivially_move_assignable<T>::value, + "Not compliant with std::is_trivially_move_assignable; " + "Standard: false, Implementation: true"); + static_assert(compliant || !std::is_trivially_move_assignable<T>::value, + "Not compliant with std::is_trivially_move_assignable; " + "Standard: true, Implementation: false"); +#endif // ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE +}; + // is_trivially_copy_assignable() // // Determines whether the passed type `T` is trivially copy assignable. |