diff options
Diffstat (limited to 'absl/meta/type_traits.h')
| -rw-r--r-- | absl/meta/type_traits.h | 314 |
1 files changed, 296 insertions, 18 deletions
diff --git a/absl/meta/type_traits.h b/absl/meta/type_traits.h index 231e08db..ae7130dd 100644 --- a/absl/meta/type_traits.h +++ b/absl/meta/type_traits.h @@ -5,7 +5,7 @@ // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // -// http://www.apache.org/licenses/LICENSE-2.0 +// https://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, @@ -22,7 +22,7 @@ // support type inference, classification, and transformation, as well as // make it easier to write templates based on generic type behavior. // -// See http://en.cppreference.com/w/cpp/header/type_traits +// See https://en.cppreference.com/w/cpp/header/type_traits // // WARNING: use of many of the constructs in this header will count as "complex // template metaprogramming", so before proceeding, please carefully consider @@ -42,10 +42,41 @@ #include "absl/base/config.h" namespace absl { -inline namespace lts_2018_12_18 { +inline namespace lts_2019_08_08 { + +// 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; @@ -194,6 +225,23 @@ struct disjunction<> : std::false_type {}; template <typename T> struct negation : std::integral_constant<bool, !T::value> {}; +// is_function() +// +// Determines whether the passed type `T` is a function type. +// +// This metafunction is designed to be a drop-in replacement for the C++11 +// `std::is_function()` metafunction for platforms that have incomplete C++11 +// support (such as libstdc++ 4.x). +// +// This metafunction works because appending `const` to a type does nothing to +// function types and reference types (and forms a const-qualified type +// otherwise). +template <typename T> +struct is_function + : std::integral_constant< + bool, !(std::is_reference<T>::value || + std::is_const<typename std::add_const<T>::type>::value)> {}; + // is_trivially_destructible() // // Determines whether the passed type `T` is trivially destructable. @@ -247,7 +295,7 @@ struct is_trivially_destructible // For the purposes of this check, the call to std::declval is considered // trivial." // -// Notes from http://en.cppreference.com/w/cpp/types/is_constructible: +// Notes from https://en.cppreference.com/w/cpp/types/is_constructible: // In many implementations, is_nothrow_constructible also checks if the // destructor throws because it is effectively noexcept(T(arg)). Same // applies to is_trivially_constructible, which, in these implementations, also @@ -276,6 +324,40 @@ 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. @@ -291,9 +373,11 @@ 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 = @@ -308,6 +392,42 @@ 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. @@ -342,6 +462,49 @@ struct is_trivially_copy_assignable #endif // ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE }; +namespace type_traits_internal { +// is_trivially_copyable() +// +// Determines whether the passed type `T` is trivially copyable. +// +// This metafunction is designed to be a drop-in replacement for the C++11 +// `std::is_trivially_copyable()` metafunction for platforms that have +// incomplete C++11 support (such as libstdc++ 4.x). We use the C++17 definition +// of TriviallyCopyable. +// +// NOTE: `is_trivially_copyable<T>::value` is `true` if all of T's copy/move +// constructors/assignment operators are trivial or deleted, T has at least +// one non-deleted copy/move constructor/assignment operator, and T is trivially +// destructible. Arrays of trivially copyable types are trivially copyable. +// +// We expose this metafunction only for internal use within absl. +template <typename T> +class is_trivially_copyable_impl { + using ExtentsRemoved = typename std::remove_all_extents<T>::type; + static constexpr bool kIsCopyOrMoveConstructible = + std::is_copy_constructible<ExtentsRemoved>::value || + std::is_move_constructible<ExtentsRemoved>::value; + static constexpr bool kIsCopyOrMoveAssignable = + absl::is_copy_assignable<ExtentsRemoved>::value || + absl::is_move_assignable<ExtentsRemoved>::value; + + public: + static constexpr bool kValue = + (__has_trivial_copy(ExtentsRemoved) || !kIsCopyOrMoveConstructible) && + (__has_trivial_assign(ExtentsRemoved) || !kIsCopyOrMoveAssignable) && + (kIsCopyOrMoveConstructible || kIsCopyOrMoveAssignable) && + is_trivially_destructible<ExtentsRemoved>::value && + // We need to check for this explicitly because otherwise we'll say + // references are trivial copyable when compiled by MSVC. + !std::is_reference<ExtentsRemoved>::value; +}; + +template <typename T> +struct is_trivially_copyable + : std::integral_constant< + bool, type_traits_internal::is_trivially_copyable_impl<T>::kValue> {}; +} // namespace type_traits_internal + // ----------------------------------------------------------------------------- // C++14 "_t" trait aliases // ----------------------------------------------------------------------------- @@ -414,25 +577,140 @@ template <typename T> using result_of_t = typename std::result_of<T>::type; namespace type_traits_internal { +// In MSVC we can't probe std::hash or stdext::hash because it triggers a +// static_assert instead of failing substitution. Libc++ prior to 4.0 +// also used a static_assert. +// +#if defined(_MSC_VER) || (defined(_LIBCPP_VERSION) && \ + _LIBCPP_VERSION < 4000 && _LIBCPP_STD_VER > 11) +#define ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_ 0 +#else +#define ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_ 1 +#endif + +#if !ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_ template <typename Key, typename = size_t> +struct IsHashable : std::true_type {}; +#else // ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_ +template <typename Key, typename = void> struct IsHashable : std::false_type {}; template <typename Key> -struct IsHashable<Key, - decltype(std::declval<std::hash<Key>>()(std::declval<Key>()))> - : std::true_type {}; +struct IsHashable< + Key, + absl::enable_if_t<std::is_convertible< + decltype(std::declval<std::hash<Key>&>()(std::declval<Key const&>())), + std::size_t>::value>> : std::true_type {}; +#endif // !ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_ + +struct AssertHashEnabledHelper { + private: + static void Sink(...) {} + struct NAT {}; + + template <class Key> + static auto GetReturnType(int) + -> decltype(std::declval<std::hash<Key>>()(std::declval<Key const&>())); + template <class Key> + static NAT GetReturnType(...); + + template <class Key> + static std::nullptr_t DoIt() { + static_assert(IsHashable<Key>::value, + "std::hash<Key> does not provide a call operator"); + static_assert( + std::is_default_constructible<std::hash<Key>>::value, + "std::hash<Key> must be default constructible when it is enabled"); + static_assert( + std::is_copy_constructible<std::hash<Key>>::value, + "std::hash<Key> must be copy constructible when it is enabled"); + static_assert(absl::is_copy_assignable<std::hash<Key>>::value, + "std::hash<Key> must be copy assignable when it is enabled"); + // is_destructible is unchecked as it's implied by each of the + // is_constructible checks. + using ReturnType = decltype(GetReturnType<Key>(0)); + static_assert(std::is_same<ReturnType, NAT>::value || + std::is_same<ReturnType, size_t>::value, + "std::hash<Key> must return size_t"); + return nullptr; + } + + template <class... Ts> + friend void AssertHashEnabled(); +}; -template <typename Key> -struct IsHashEnabled - : absl::conjunction<std::is_default_constructible<std::hash<Key>>, - std::is_copy_constructible<std::hash<Key>>, - std::is_destructible<std::hash<Key>>, - absl::is_copy_assignable<std::hash<Key>>, - IsHashable<Key>> {}; +template <class... Ts> +inline void AssertHashEnabled() { + using Helper = AssertHashEnabledHelper; + Helper::Sink(Helper::DoIt<Ts>()...); +} } // namespace type_traits_internal -} // inline namespace lts_2018_12_18 +// An internal namespace that is required to implement the C++17 swap traits. +// It is not further nested in type_traits_internal to avoid long symbol names. +namespace swap_internal { + +// Necessary for the traits. +using std::swap; + +// This declaration prevents global `swap` and `absl::swap` overloads from being +// considered unless ADL picks them up. +void swap(); + +template <class T> +using IsSwappableImpl = decltype(swap(std::declval<T&>(), std::declval<T&>())); + +// NOTE: This dance with the default template parameter is for MSVC. +template <class T, + class IsNoexcept = std::integral_constant< + bool, noexcept(swap(std::declval<T&>(), std::declval<T&>()))>> +using IsNothrowSwappableImpl = typename std::enable_if<IsNoexcept::value>::type; + +// IsSwappable +// +// Determines whether the standard swap idiom is a valid expression for +// arguments of type `T`. +template <class T> +struct IsSwappable + : absl::type_traits_internal::is_detected<IsSwappableImpl, T> {}; + +// IsNothrowSwappable +// +// Determines whether the standard swap idiom is a valid expression for +// arguments of type `T` and is noexcept. +template <class T> +struct IsNothrowSwappable + : absl::type_traits_internal::is_detected<IsNothrowSwappableImpl, T> {}; + +// Swap() +// +// Performs the swap idiom from a namespace where valid candidates may only be +// found in `std` or via ADL. +template <class T, absl::enable_if_t<IsSwappable<T>::value, int> = 0> +void Swap(T& lhs, T& rhs) noexcept(IsNothrowSwappable<T>::value) { + swap(lhs, rhs); +} + +// StdSwapIsUnconstrained +// +// Some standard library implementations are broken in that they do not +// constrain `std::swap`. This will effectively tell us if we are dealing with +// one of those implementations. +using StdSwapIsUnconstrained = IsSwappable<void()>; + +} // namespace swap_internal + +namespace type_traits_internal { + +// Make the swap-related traits/function accessible from this namespace. +using swap_internal::IsNothrowSwappable; +using swap_internal::IsSwappable; +using swap_internal::Swap; +using swap_internal::StdSwapIsUnconstrained; + +} // namespace type_traits_internal +} // inline namespace lts_2019_08_08 } // namespace absl #endif // ABSL_META_TYPE_TRAITS_H_ |