From aa844899c937bde5d2b24f276b59997e5b668bde Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Thu, 8 Aug 2019 10:56:58 -0700 Subject: Creation of LTS branch "lts_2019_08_08" - 9ee91d3e430fb33a4590486573792eb0fa146c2d Export of internal Abseil changes by Abseil Team - 8efba58a3b656e9b41fb0471ae6453425a61c520 Export of internal Abseil changes by Abseil Team - b49b8d16b67ec6912899684b732e6367f258cfdb Export of internal Abseil changes by Abseil Team - 67222ffc4c83d918ce8395aa61769eeb77df4c4d Export of internal Abseil changes by Abseil Team - c5c4db4f5191fe5e76cbf68dcc71fb28702f7d2b Export of internal Abseil changes by Abseil Team - 14550beb3b7b97195e483fb74b5efb906395c31e Export of internal Abseil changes. by Abseil Team - 52e88ee56b72cf32bc66534d942c7398ce481331 Export of internal Abseil changes. by Abseil Team - 36d37ab992038f52276ca66b9da80c1cf0f57dc2 Export of internal Abseil changes. by Abseil Team - ad1485c8986246b2ae9105e512738d0e97aec887 Export of internal Abseil changes. by Abseil Team - 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968a34ffdaadd7db062a9621dfbdf8b2d16e05af Export of internal Abseil changes. by Abseil Team - 3e2e9b5557e76d098de4b8a2a659125b98ca519b Merge pull request #231 from uilianries/feature/conan by Mark Barolak - 111ca7060a6ff50115ca85b59f6b5d8c8c5e9105 Export of internal Abseil changes. by Abseil Team - 389ec3f906f018661a5308458d623d01f96d7b23 Export of internal Abseil changes. by Abseil Team - 8fbcdb90952c57828c4a9c2f6d79fcd7cae9088f Export of internal Abseil changes. by Abseil Team - 455dc17ba1af9635f0b60155bc565bc572a1e722 Export of internal Abseil changes. by Abseil Team - f197d7c72a54064cfde5a2058f1513a4a0ee36fb Export of internal Abseil changes. by Abseil Team - 284378a71b32dfb3af4e3661f585e671d1b603a3 Export of internal Abseil changes. by Abseil Team GitOrigin-RevId: 9ee91d3e430fb33a4590486573792eb0fa146c2d Change-Id: Ia06e548bc106cc9d136f6c65714be6645317aced --- absl/meta/type_traits.h | 314 +++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 296 insertions(+), 18 deletions(-) (limited to 'absl/meta/type_traits.h') 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 +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 +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 +struct IsTriviallyMoveAssignableReference : std::false_type {}; + +template +struct IsTriviallyMoveAssignableReference + : absl::is_trivially_move_assignable::type {}; + +template +struct IsTriviallyMoveAssignableReference + : absl::is_trivially_move_assignable::type {}; + template struct VoidTImpl { using type = void; @@ -194,6 +225,23 @@ struct disjunction<> : std::false_type {}; template struct negation : std::integral_constant {}; +// 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 +struct is_function + : std::integral_constant< + bool, !(std::is_reference::value || + std::is_const::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());` needs to be well-formed and not call any +// nontrivial operation. Nontrivially destructible types will cause the +// expression to be nontrivial. +template +struct is_trivially_move_constructible + : std::conditional< + std::is_object::value && !std::is_array::value, + std::is_move_constructible< + type_traits_internal::SingleMemberUnion>, + std::is_reference>::type::type { +#ifdef ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE + private: + static constexpr bool compliant = + std::is_trivially_move_constructible::value == + is_trivially_move_constructible::value; + static_assert(compliant || std::is_trivially_move_constructible::value, + "Not compliant with std::is_trivially_move_constructible; " + "Standard: false, Implementation: true"); + static_assert(compliant || !std::is_trivially_move_constructible::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 struct is_trivially_copy_constructible - : std::integral_constant::value && - is_trivially_destructible::value> { + : std::conditional< + std::is_object::value && !std::is_array::value, + std::is_copy_constructible< + type_traits_internal::SingleMemberUnion>, + std::is_lvalue_reference>::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::value` is `true` if the expression +// `declval() = declval()` is well-formed when treated as an unevaluated +// operand. `is_trivially_assignable` requires the assignment to call no +// operation that is not trivial. `is_trivially_copy_assignable` is simply +// `is_trivially_assignable`. +template +struct is_trivially_move_assignable + : std::conditional< + std::is_object::value && !std::is_array::value, + std::is_move_assignable>, + type_traits_internal::IsTriviallyMoveAssignableReference>::type:: + type { +#ifdef ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE + private: + static constexpr bool compliant = + std::is_trivially_move_assignable::value == + is_trivially_move_assignable::value; + static_assert(compliant || std::is_trivially_move_assignable::value, + "Not compliant with std::is_trivially_move_assignable; " + "Standard: false, Implementation: true"); + static_assert(compliant || !std::is_trivially_move_assignable::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::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 +class is_trivially_copyable_impl { + using ExtentsRemoved = typename std::remove_all_extents::type; + static constexpr bool kIsCopyOrMoveConstructible = + std::is_copy_constructible::value || + std::is_move_constructible::value; + static constexpr bool kIsCopyOrMoveAssignable = + absl::is_copy_assignable::value || + absl::is_move_assignable::value; + + public: + static constexpr bool kValue = + (__has_trivial_copy(ExtentsRemoved) || !kIsCopyOrMoveConstructible) && + (__has_trivial_assign(ExtentsRemoved) || !kIsCopyOrMoveAssignable) && + (kIsCopyOrMoveConstructible || kIsCopyOrMoveAssignable) && + is_trivially_destructible::value && + // We need to check for this explicitly because otherwise we'll say + // references are trivial copyable when compiled by MSVC. + !std::is_reference::value; +}; + +template +struct is_trivially_copyable + : std::integral_constant< + bool, type_traits_internal::is_trivially_copyable_impl::kValue> {}; +} // namespace type_traits_internal + // ----------------------------------------------------------------------------- // C++14 "_t" trait aliases // ----------------------------------------------------------------------------- @@ -414,25 +577,140 @@ template using result_of_t = typename std::result_of::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 +struct IsHashable : std::true_type {}; +#else // ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_ +template struct IsHashable : std::false_type {}; template -struct IsHashable>()(std::declval()))> - : std::true_type {}; +struct IsHashable< + Key, + absl::enable_if_t&>()(std::declval())), + std::size_t>::value>> : std::true_type {}; +#endif // !ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_ + +struct AssertHashEnabledHelper { + private: + static void Sink(...) {} + struct NAT {}; + + template + static auto GetReturnType(int) + -> decltype(std::declval>()(std::declval())); + template + static NAT GetReturnType(...); + + template + static std::nullptr_t DoIt() { + static_assert(IsHashable::value, + "std::hash does not provide a call operator"); + static_assert( + std::is_default_constructible>::value, + "std::hash must be default constructible when it is enabled"); + static_assert( + std::is_copy_constructible>::value, + "std::hash must be copy constructible when it is enabled"); + static_assert(absl::is_copy_assignable>::value, + "std::hash 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(0)); + static_assert(std::is_same::value || + std::is_same::value, + "std::hash must return size_t"); + return nullptr; + } + + template + friend void AssertHashEnabled(); +}; -template -struct IsHashEnabled - : absl::conjunction>, - std::is_copy_constructible>, - std::is_destructible>, - absl::is_copy_assignable>, - IsHashable> {}; +template +inline void AssertHashEnabled() { + using Helper = AssertHashEnabledHelper; + Helper::Sink(Helper::DoIt()...); +} } // 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 +using IsSwappableImpl = decltype(swap(std::declval(), std::declval())); + +// NOTE: This dance with the default template parameter is for MSVC. +template (), std::declval()))>> +using IsNothrowSwappableImpl = typename std::enable_if::type; + +// IsSwappable +// +// Determines whether the standard swap idiom is a valid expression for +// arguments of type `T`. +template +struct IsSwappable + : absl::type_traits_internal::is_detected {}; + +// IsNothrowSwappable +// +// Determines whether the standard swap idiom is a valid expression for +// arguments of type `T` and is noexcept. +template +struct IsNothrowSwappable + : absl::type_traits_internal::is_detected {}; + +// Swap() +// +// Performs the swap idiom from a namespace where valid candidates may only be +// found in `std` or via ADL. +template ::value, int> = 0> +void Swap(T& lhs, T& rhs) noexcept(IsNothrowSwappable::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; + +} // 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_ -- cgit v1.2.3