1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
|
// 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, Rank2{});
}
// 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, Rank2{})),
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:
// Use go/ranked-overloads for dispatching.
struct Rank0 {};
struct Rank1 : Rank0 {};
struct Rank2 : 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,
Rank2) -> 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, Rank0) {
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_
|
