diff options
Diffstat (limited to 'third_party/abseil_cpp/absl/container/internal/hash_policy_traits.h')
-rw-r--r-- | third_party/abseil_cpp/absl/container/internal/hash_policy_traits.h | 31 |
1 files changed, 24 insertions, 7 deletions
diff --git a/third_party/abseil_cpp/absl/container/internal/hash_policy_traits.h b/third_party/abseil_cpp/absl/container/internal/hash_policy_traits.h index 3e1209c6ebec..46c97b18a227 100644 --- a/third_party/abseil_cpp/absl/container/internal/hash_policy_traits.h +++ b/third_party/abseil_cpp/absl/container/internal/hash_policy_traits.h @@ -17,6 +17,7 @@ #include <cstddef> #include <memory> +#include <new> #include <type_traits> #include <utility> @@ -29,15 +30,34 @@ namespace container_internal { // Defines how slots are initialized/destroyed/moved. template <class Policy, class = void> struct hash_policy_traits { + // The type of the keys stored in the hashtable. + using key_type = typename Policy::key_type; + private: struct ReturnKey { - // We return `Key` here. + // When C++17 is available, we can use std::launder to provide mutable + // access to the key for use in node handle. +#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606 + template <class Key, + absl::enable_if_t<std::is_lvalue_reference<Key>::value, int> = 0> + static key_type& Impl(Key&& k, int) { + return *std::launder( + const_cast<key_type*>(std::addressof(std::forward<Key>(k)))); + } +#endif + + template <class Key> + static Key Impl(Key&& k, char) { + return std::forward<Key>(k); + } + // When Key=T&, we forward the lvalue reference. // When Key=T, we return by value to avoid a dangling reference. // eg, for string_hash_map. template <class Key, class... Args> - Key operator()(Key&& k, const Args&...) const { - return std::forward<Key>(k); + auto operator()(Key&& k, const Args&...) const + -> decltype(Impl(std::forward<Key>(k), 0)) { + return Impl(std::forward<Key>(k), 0); } }; @@ -52,9 +72,6 @@ struct hash_policy_traits { // The actual object stored in the hash table. using slot_type = typename Policy::slot_type; - // The type of the keys stored in the hashtable. - using key_type = typename Policy::key_type; - // The argument type for insertions into the hashtable. This is different // from value_type for increased performance. See initializer_list constructor // and insert() member functions for more details. @@ -156,7 +173,7 @@ struct hash_policy_traits { // Returns the "key" portion of the slot. // Used for node handle manipulation. template <class P = Policy> - static auto key(slot_type* slot) + static auto mutable_key(slot_type* slot) -> decltype(P::apply(ReturnKey(), element(slot))) { return P::apply(ReturnKey(), element(slot)); } |