diff options
Diffstat (limited to 'absl/hash/internal/hash.h')
| -rw-r--r-- | absl/hash/internal/hash.h | 161 |
1 files changed, 63 insertions, 98 deletions
diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h index 2a45bc84..9ab98901 100644 --- a/absl/hash/internal/hash.h +++ b/absl/hash/internal/hash.h @@ -535,20 +535,6 @@ hash_range_or_bytes(H hash_state, const T* data, size_t size) { return hash_state; } -// InvokeHashTag -// -// InvokeHash(H, const T&) invokes the appropriate hash implementation for a -// hasher of type `H` and a value of type `T`. If `T` is not hashable, there -// will be no matching overload of InvokeHash(). -// Note: Some platforms (eg MSVC) do not support the detect idiom on -// std::hash. In those platforms the last fallback will be std::hash and -// InvokeHash() will always have a valid overload even if std::hash<T> is not -// valid. -// -// We try the following options in order: -// * If is_uniquely_represented, hash bytes directly. -// * ADL AbslHashValue(H, const T&) call. -// * std::hash<T> #if defined(ABSL_INTERNAL_LEGACY_HASH_NAMESPACE) && \ ABSL_META_INTERNAL_STD_HASH_SFINAE_FRIENDLY_ #define ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ 1 @@ -556,23 +542,15 @@ hash_range_or_bytes(H hash_state, const T* data, size_t size) { #define ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ 0 #endif -enum class InvokeHashTag { - kUniquelyRepresented, - kHashValue, -#if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ - kLegacyHash, -#endif // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ - kStdHash, - kNone -}; - // HashSelect // // Type trait to select the appropriate hash implementation to use. -// HashSelect<T>::value is an instance of InvokeHashTag that indicates the best -// available hashing mechanism. -// See `Note` above about MSVC. -template <typename T> +// HashSelect::type<T> will give the proper hash implementation, to be invoked +// as: +// HashSelect::type<T>::Invoke(state, value) +// Also, HashSelect::type<T>::value is a boolean equal to `true` if there is a +// valid `Invoke` function. Types that are not hashable will have a ::value of +// `false`. struct HashSelect { private: struct State : HashStateBase<State> { @@ -581,89 +559,75 @@ struct HashSelect { using State::HashStateBase::combine_contiguous; }; - // `Probe<V, Tag>::value` evaluates to `V<T>::value` if it is a valid - // expression, and `false` otherwise. - // `Probe<V, Tag>::tag` always evaluates to `Tag`. - template <template <typename> class V, InvokeHashTag Tag> - struct Probe { - private: - template <typename U, typename std::enable_if<V<U>::value, int>::type = 0> - static std::true_type Test(int); - template <typename U> - static std::false_type Test(char); - - public: - static constexpr InvokeHashTag kTag = Tag; - static constexpr bool value = decltype( - Test<absl::remove_const_t<absl::remove_reference_t<T>>>(0))::value; + struct UniquelyRepresentedProbe { + template <typename H, typename T> + static auto Invoke(H state, const T& value) + -> absl::enable_if_t<is_uniquely_represented<T>::value, H> { + return hash_internal::hash_bytes(std::move(state), value); + } }; - template <typename U> - using ProbeUniquelyRepresented = is_uniquely_represented<U>; - - template <typename U> - using ProbeHashValue = - std::is_same<State, decltype(AbslHashValue(std::declval<State>(), - std::declval<const U&>()))>; + struct HashValueProbe { + template <typename H, typename T> + static auto Invoke(H state, const T& value) -> absl::enable_if_t< + std::is_same<H, + decltype(AbslHashValue(std::move(state), value))>::value, + H> { + return AbslHashValue(std::move(state), value); + } + }; + struct LegacyHashProbe { #if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ - template <typename U> - using ProbeLegacyHash = - std::is_convertible<decltype(ABSL_INTERNAL_LEGACY_HASH_NAMESPACE::hash< - U>()(std::declval<const U&>())), - size_t>; + template <typename H, typename T> + static auto Invoke(H state, const T& value) -> absl::enable_if_t< + std::is_convertible< + decltype(ABSL_INTERNAL_LEGACY_HASH_NAMESPACE::hash<T>()(value)), + size_t>::value, + H> { + return hash_internal::hash_bytes( + std::move(state), + ABSL_INTERNAL_LEGACY_HASH_NAMESPACE::hash<T>{}(value)); + } #endif // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ + }; - template <typename U> - using ProbeStdHash = absl::type_traits_internal::IsHashable<U>; + struct StdHashProbe { + template <typename H, typename T> + static auto Invoke(H state, const T& value) + -> absl::enable_if_t<type_traits_internal::IsHashable<T>::value, H> { + return hash_internal::hash_bytes(std::move(state), std::hash<T>{}(value)); + } + }; - template <typename U> - using ProbeNone = std::true_type; + template <typename Hash, typename T> + struct Probe : Hash { + private: + template <typename H, typename = decltype(H::Invoke( + std::declval<State>(), std::declval<const T&>()))> + static std::true_type Test(int); + template <typename U> + static std::false_type Test(char); + + public: + static constexpr bool value = decltype(Test<Hash>(0))::value; + }; public: // Probe each implementation in order. // disjunction provides short circuting wrt instantiation. - static constexpr InvokeHashTag value = absl::disjunction< - Probe<ProbeUniquelyRepresented, InvokeHashTag::kUniquelyRepresented>, - Probe<ProbeHashValue, InvokeHashTag::kHashValue>, -#if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ - Probe<ProbeLegacyHash, InvokeHashTag::kLegacyHash>, -#endif // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ - Probe<ProbeStdHash, InvokeHashTag::kStdHash>, - Probe<ProbeNone, InvokeHashTag::kNone>>::kTag; + template <typename T> + using Apply = absl::disjunction< // + Probe<UniquelyRepresentedProbe, T>, // + Probe<HashValueProbe, T>, // + Probe<LegacyHashProbe, T>, // + Probe<StdHashProbe, T>, // + std::false_type>; }; template <typename T> -struct is_hashable : std::integral_constant<bool, HashSelect<T>::value != - InvokeHashTag::kNone> {}; - -template <typename H, typename T> -absl::enable_if_t<HashSelect<T>::value == InvokeHashTag::kUniquelyRepresented, - H> -InvokeHash(H state, const T& value) { - return hash_internal::hash_bytes(std::move(state), value); -} - -template <typename H, typename T> -absl::enable_if_t<HashSelect<T>::value == InvokeHashTag::kHashValue, H> -InvokeHash(H state, const T& value) { - return AbslHashValue(std::move(state), value); -} - -#if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ -template <typename H, typename T> -absl::enable_if_t<HashSelect<T>::value == InvokeHashTag::kLegacyHash, H> -InvokeHash(H state, const T& value) { - return hash_internal::hash_bytes( - std::move(state), ABSL_INTERNAL_LEGACY_HASH_NAMESPACE::hash<T>{}(value)); -} -#endif // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ - -template <typename H, typename T> -absl::enable_if_t<HashSelect<T>::value == InvokeHashTag::kStdHash, H> -InvokeHash(H state, const T& value) { - return hash_internal::hash_bytes(std::move(state), std::hash<T>{}(value)); -} +struct is_hashable + : std::integral_constant<bool, HashSelect::template Apply<T>::value> {}; // CityHashState class CityHashState : public HashStateBase<CityHashState> { @@ -873,7 +837,8 @@ struct Hash template <typename H> template <typename T, typename... Ts> H HashStateBase<H>::combine(H state, const T& value, const Ts&... values) { - return H::combine(hash_internal::InvokeHash(std::move(state), value), + return H::combine(hash_internal::HashSelect::template Apply<T>::Invoke( + std::move(state), value), values...); } |