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// Copyright 2022 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef ABSL_CONTAINER_INTERNAL_COMMON_POLICY_TRAITS_H_
#define ABSL_CONTAINER_INTERNAL_COMMON_POLICY_TRAITS_H_
#include <cstddef>
#include <cstring>
#include <memory>
#include <new>
#include <type_traits>
#include <utility>
#include "absl/meta/type_traits.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace container_internal {
// Defines how slots are initialized/destroyed/moved.
template <class Policy, class = void>
struct common_policy_traits {
// The actual object stored in the container.
using slot_type = typename Policy::slot_type;
using reference = decltype(Policy::element(std::declval<slot_type*>()));
using value_type = typename std::remove_reference<reference>::type;
// PRECONDITION: `slot` is UNINITIALIZED
// POSTCONDITION: `slot` is INITIALIZED
template <class Alloc, class... Args>
static void construct(Alloc* alloc, slot_type* slot, Args&&... args) {
Policy::construct(alloc, slot, std::forward<Args>(args)...);
}
// PRECONDITION: `slot` is INITIALIZED
// POSTCONDITION: `slot` is UNINITIALIZED
// Returns std::true_type in case destroy is trivial.
template <class Alloc>
static auto destroy(Alloc* alloc, slot_type* slot) {
return Policy::destroy(alloc, slot);
}
// Transfers the `old_slot` to `new_slot`. Any memory allocated by the
// allocator inside `old_slot` to `new_slot` can be transferred.
//
// OPTIONAL: defaults to:
//
// clone(new_slot, std::move(*old_slot));
// destroy(old_slot);
//
// PRECONDITION: `new_slot` is UNINITIALIZED and `old_slot` is INITIALIZED
// POSTCONDITION: `new_slot` is INITIALIZED and `old_slot` is
// UNINITIALIZED
template <class Alloc>
static void transfer(Alloc* alloc, slot_type* new_slot, slot_type* old_slot) {
transfer_impl(alloc, new_slot, old_slot, Rank0{});
}
// PRECONDITION: `slot` is INITIALIZED
// POSTCONDITION: `slot` is INITIALIZED
// Note: we use remove_const_t so that the two overloads have different args
// in the case of sets with explicitly const value_types.
template <class P = Policy>
static auto element(absl::remove_const_t<slot_type>* slot)
-> decltype(P::element(slot)) {
return P::element(slot);
}
template <class P = Policy>
static auto element(const slot_type* slot) -> decltype(P::element(slot)) {
return P::element(slot);
}
static constexpr bool transfer_uses_memcpy() {
return std::is_same<decltype(transfer_impl<std::allocator<char>>(
nullptr, nullptr, nullptr, Rank0{})),
std::true_type>::value;
}
// Returns true if destroy is trivial and can be omitted.
template <class Alloc>
static constexpr bool destroy_is_trivial() {
return std::is_same<decltype(destroy<Alloc>(nullptr, nullptr)),
std::true_type>::value;
}
private:
// To rank the overloads below for overload resolution. Rank0 is preferred.
struct Rank2 {};
struct Rank1 : Rank2 {};
struct Rank0 : Rank1 {};
// Use auto -> decltype as an enabler.
// P::transfer returns std::true_type if transfer uses memcpy (e.g. in
// node_slot_policy).
template <class Alloc, class P = Policy>
static auto transfer_impl(Alloc* alloc, slot_type* new_slot,
slot_type* old_slot, Rank0)
-> decltype(P::transfer(alloc, new_slot, old_slot)) {
return P::transfer(alloc, new_slot, old_slot);
}
#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606
// This overload returns true_type for the trait below.
// The conditional_t is to make the enabler type dependent.
template <class Alloc,
typename = std::enable_if_t<absl::is_trivially_relocatable<
std::conditional_t<false, Alloc, value_type>>::value>>
static std::true_type transfer_impl(Alloc*, slot_type* new_slot,
slot_type* old_slot, Rank1) {
// TODO(b/247130232): remove casts after fixing warnings.
// TODO(b/251814870): remove casts after fixing warnings.
std::memcpy(
static_cast<void*>(std::launder(
const_cast<std::remove_const_t<value_type>*>(&element(new_slot)))),
static_cast<const void*>(&element(old_slot)), sizeof(value_type));
return {};
}
#endif
template <class Alloc>
static void transfer_impl(Alloc* alloc, slot_type* new_slot,
slot_type* old_slot, Rank2) {
construct(alloc, new_slot, std::move(element(old_slot)));
destroy(alloc, old_slot);
}
};
} // namespace container_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_CONTAINER_INTERNAL_COMMON_POLICY_TRAITS_H_
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