diff options
Diffstat (limited to 'absl/container/internal/compressed_tuple.h')
| -rw-r--r-- | absl/container/internal/compressed_tuple.h | 78 |
1 files changed, 58 insertions, 20 deletions
diff --git a/absl/container/internal/compressed_tuple.h b/absl/container/internal/compressed_tuple.h index bb3471f5d747..1713ad6862c5 100644 --- a/absl/container/internal/compressed_tuple.h +++ b/absl/container/internal/compressed_tuple.h @@ -32,6 +32,7 @@ #ifndef ABSL_CONTAINER_INTERNAL_COMPRESSED_TUPLE_H_ #define ABSL_CONTAINER_INTERNAL_COMPRESSED_TUPLE_H_ +#include <initializer_list> #include <tuple> #include <type_traits> #include <utility> @@ -75,17 +76,30 @@ constexpr bool IsFinal() { #endif } +// We can't use EBCO on other CompressedTuples because that would mean that we +// derive from multiple Storage<> instantiations with the same I parameter, +// and potentially from multiple identical Storage<> instantiations. So anytime +// we use type inheritance rather than encapsulation, we mark +// CompressedTupleImpl, to make this easy to detect. +struct uses_inheritance {}; + template <typename T> constexpr bool ShouldUseBase() { - return std::is_class<T>::value && std::is_empty<T>::value && !IsFinal<T>(); + return std::is_class<T>::value && std::is_empty<T>::value && !IsFinal<T>() && + !std::is_base_of<uses_inheritance, T>::value; } // The storage class provides two specializations: // - For empty classes, it stores T as a base class. // - For everything else, it stores T as a member. -template <typename D, size_t I, bool = ShouldUseBase<ElemT<D, I>>()> +template <typename T, size_t I, +#if defined(_MSC_VER) + bool UseBase = + ShouldUseBase<typename std::enable_if<true, T>::type>()> +#else + bool UseBase = ShouldUseBase<T>()> +#endif struct Storage { - using T = ElemT<D, I>; T value; constexpr Storage() = default; explicit constexpr Storage(T&& v) : value(absl::forward<T>(v)) {} @@ -95,10 +109,8 @@ struct Storage { T&& get() && { return std::move(*this).value; } }; -template <typename D, size_t I> -struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC Storage<D, I, true> - : ElemT<D, I> { - using T = internal_compressed_tuple::ElemT<D, I>; +template <typename T, size_t I> +struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC Storage<T, I, true> : T { constexpr Storage() = default; explicit constexpr Storage(T&& v) : T(absl::forward<T>(v)) {} constexpr const T& get() const& { return *this; } @@ -107,29 +119,54 @@ struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC Storage<D, I, true> T&& get() && { return std::move(*this); } }; -template <typename D, typename I> +template <typename D, typename I, bool ShouldAnyUseBase> struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTupleImpl; -template <typename... Ts, size_t... I> -struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC - CompressedTupleImpl<CompressedTuple<Ts...>, absl::index_sequence<I...>> +template <typename... Ts, size_t... I, bool ShouldAnyUseBase> +struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTupleImpl< + CompressedTuple<Ts...>, absl::index_sequence<I...>, ShouldAnyUseBase> // We use the dummy identity function through std::integral_constant to // convince MSVC of accepting and expanding I in that context. Without it // you would get: // error C3548: 'I': parameter pack cannot be used in this context - : Storage<CompressedTuple<Ts...>, - std::integral_constant<size_t, I>::value>... { + : uses_inheritance, + Storage<Ts, std::integral_constant<size_t, I>::value>... { + constexpr CompressedTupleImpl() = default; + explicit constexpr CompressedTupleImpl(Ts&&... args) + : Storage<Ts, I>(absl::forward<Ts>(args))... {} + friend CompressedTuple<Ts...>; +}; + +template <typename... Ts, size_t... I> +struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTupleImpl< + CompressedTuple<Ts...>, absl::index_sequence<I...>, false> + // We use the dummy identity function as above... + : Storage<Ts, std::integral_constant<size_t, I>::value, false>... { constexpr CompressedTupleImpl() = default; explicit constexpr CompressedTupleImpl(Ts&&... args) - : Storage<CompressedTuple<Ts...>, I>(absl::forward<Ts>(args))... {} + : Storage<Ts, I, false>(absl::forward<Ts>(args))... {} + friend CompressedTuple<Ts...>; }; +std::false_type Or(std::initializer_list<std::false_type>); +std::true_type Or(std::initializer_list<bool>); + +// MSVC requires this to be done separately rather than within the declaration +// of CompressedTuple below. +template <typename... Ts> +constexpr bool ShouldAnyUseBase() { + return decltype( + Or({std::integral_constant<bool, ShouldUseBase<Ts>()>()...})){}; +} + } // namespace internal_compressed_tuple // Helper class to perform the Empty Base Class Optimization. // Ts can contain classes and non-classes, empty or not. For the ones that // are empty classes, we perform the CompressedTuple. If all types in Ts are -// empty classes, then CompressedTuple<Ts...> is itself an empty class. +// empty classes, then CompressedTuple<Ts...> is itself an empty class. (This +// does not apply when one or more of those empty classes is itself an empty +// CompressedTuple.) // // To access the members, use member .get<N>() function. // @@ -145,7 +182,8 @@ struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC template <typename... Ts> class ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTuple : private internal_compressed_tuple::CompressedTupleImpl< - CompressedTuple<Ts...>, absl::index_sequence_for<Ts...>> { + CompressedTuple<Ts...>, absl::index_sequence_for<Ts...>, + internal_compressed_tuple::ShouldAnyUseBase<Ts...>()> { private: template <int I> using ElemT = internal_compressed_tuple::ElemT<CompressedTuple, I>; @@ -157,24 +195,24 @@ class ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTuple template <int I> ElemT<I>& get() & { - return internal_compressed_tuple::Storage<CompressedTuple, I>::get(); + return internal_compressed_tuple::Storage<ElemT<I>, I>::get(); } template <int I> constexpr const ElemT<I>& get() const& { - return internal_compressed_tuple::Storage<CompressedTuple, I>::get(); + return internal_compressed_tuple::Storage<ElemT<I>, I>::get(); } template <int I> ElemT<I>&& get() && { return std::move(*this) - .internal_compressed_tuple::template Storage<CompressedTuple, I>::get(); + .internal_compressed_tuple::template Storage<ElemT<I>, I>::get(); } template <int I> constexpr const ElemT<I>&& get() const&& { return absl::move(*this) - .internal_compressed_tuple::template Storage<CompressedTuple, I>::get(); + .internal_compressed_tuple::template Storage<ElemT<I>, I>::get(); } }; |