| // Copyright 2020 the V8 project authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef INCLUDE_CPPGC_TYPE_TRAITS_H_ |
| #define INCLUDE_CPPGC_TYPE_TRAITS_H_ |
| |
| #include <type_traits> |
| |
| namespace cppgc { |
| |
| class Visitor; |
| |
| namespace internal { |
| |
| // Pre-C++17 custom implementation of std::void_t. |
| template <typename... Ts> |
| struct make_void { |
| typedef void type; |
| }; |
| template <typename... Ts> |
| using void_t = typename make_void<Ts...>::type; |
| |
| // Not supposed to be specialized by the user. |
| template <typename T> |
| struct IsWeak : std::false_type {}; |
| |
| template <typename T, template <typename... V> class U> |
| struct IsSubclassOfTemplate { |
| private: |
| template <typename... W> |
| static std::true_type SubclassCheck(U<W...>*); |
| static std::false_type SubclassCheck(...); |
| |
| public: |
| static constexpr bool value = |
| decltype(SubclassCheck(std::declval<T*>()))::value; |
| }; |
| |
| // IsTraceMethodConst is used to verify that all Trace methods are marked as |
| // const. It is equivalent to IsTraceable but for a non-const object. |
| template <typename T, typename = void> |
| struct IsTraceMethodConst : std::false_type {}; |
| |
| template <typename T> |
| struct IsTraceMethodConst<T, void_t<decltype(std::declval<const T>().Trace( |
| std::declval<Visitor*>()))>> : std::true_type { |
| }; |
| |
| template <typename T, typename = void> |
| struct IsTraceable : std::false_type { |
| static_assert(sizeof(T), "T must be fully defined"); |
| }; |
| |
| template <typename T> |
| struct IsTraceable< |
| T, void_t<decltype(std::declval<T>().Trace(std::declval<Visitor*>()))>> |
| : std::true_type { |
| // All Trace methods should be marked as const. If an object of type |
| // 'T' is traceable then any object of type 'const T' should also |
| // be traceable. |
| static_assert(IsTraceMethodConst<T>(), |
| "Trace methods should be marked as const."); |
| }; |
| |
| template <typename T> |
| constexpr bool IsTraceableV = IsTraceable<T>::value; |
| |
| template <typename T, typename = void> |
| struct IsGarbageCollectedMixinType : std::false_type { |
| static_assert(sizeof(T), "T must be fully defined"); |
| }; |
| |
| template <typename T> |
| struct IsGarbageCollectedMixinType< |
| T, |
| void_t<typename std::remove_const_t<T>::IsGarbageCollectedMixinTypeMarker>> |
| : std::true_type { |
| static_assert(sizeof(T), "T must be fully defined"); |
| }; |
| |
| template <typename T, typename = void> |
| struct IsGarbageCollectedType : IsGarbageCollectedMixinType<T> { |
| static_assert(sizeof(T), "T must be fully defined"); |
| }; |
| |
| template <typename T> |
| struct IsGarbageCollectedType< |
| T, void_t<typename std::remove_const_t<T>::IsGarbageCollectedTypeMarker>> |
| : std::true_type { |
| static_assert(sizeof(T), "T must be fully defined"); |
| }; |
| |
| template <typename T> |
| constexpr bool IsGarbageCollectedTypeV = |
| internal::IsGarbageCollectedType<T>::value; |
| |
| template <typename T> |
| constexpr bool IsGarbageCollectedMixinTypeV = |
| internal::IsGarbageCollectedMixinType<T>::value; |
| |
| } // namespace internal |
| |
| template <typename T> |
| constexpr bool IsWeakV = internal::IsWeak<T>::value; |
| |
| } // namespace cppgc |
| |
| #endif // INCLUDE_CPPGC_TYPE_TRAITS_H_ |