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
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
|
// Copyright 2017 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
//
// http://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.
//
// This header file contains C++11 versions of standard <utility> header
// abstractions available within C++14 and C++17, and are designed to be drop-in
// replacement for code compliant with C++14 and C++17.
//
// The following abstractions are defined:
//
// * integer_sequence<T, Ints...> == std::integer_sequence<T, Ints...>
// * index_sequence<Ints...> == std::index_sequence<Ints...>
// * make_integer_sequence<T, N> == std::make_integer_sequence<T, N>
// * make_index_sequence<N> == std::make_index_sequence<N>
// * index_sequence_for<Ts...> == std::index_sequence_for<Ts...>
//
// This header file also provides the tag types `in_place_t`, `in_place_type_t`,
// and `in_place_index_t`, as well as the constant `in_place`, and
// `constexpr` `std::move()` and `std::forward()` implementations in C++11.
//
// References:
//
// http://en.cppreference.com/w/cpp/utility/integer_sequence
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3658.html
//
//
// Example:
// // Unpack a tuple for use as a function call's argument list.
//
// template <typename F, typename Tup, size_t... Is>
// auto Impl(F f, const Tup& tup, absl::index_sequence<Is...>)
// -> decltype(f(std::get<Is>(tup) ...)) {
// return f(std::get<Is>(tup) ...);
// }
//
// template <typename Tup>
// using TupIdxSeq = absl::make_index_sequence<std::tuple_size<Tup>::value>;
//
// template <typename F, typename Tup>
// auto ApplyFromTuple(F f, const Tup& tup)
// -> decltype(Impl(f, tup, TupIdxSeq<Tup>{})) {
// return Impl(f, tup, TupIdxSeq<Tup>{});
// }
#ifndef ABSL_UTILITY_UTILITY_H_
#define ABSL_UTILITY_UTILITY_H_
#include <cstddef>
#include <cstdlib>
#include <utility>
#include "absl/base/config.h"
#include "absl/meta/type_traits.h"
namespace absl {
// integer_sequence
//
// Class template representing a compile-time integer sequence. An instantiation
// of `integer_sequence<T, Ints...>` has a sequence of integers encoded in its
// type through its template arguments (which is a common need when
// working with C++11 variadic templates). `absl::integer_sequence` is designed
// to be a drop-in replacement for C++14's `std::integer_sequence`.
//
// Example:
//
// template< class T, T... Ints >
// void user_function(integer_sequence<T, Ints...>);
//
// int main()
// {
// // user_function's `T` will be deduced to `int` and `Ints...`
// // will be deduced to `0, 1, 2, 3, 4`.
// user_function(make_integer_sequence<int, 5>());
// }
template <typename T, T... Ints>
struct integer_sequence {
using value_type = T;
static constexpr size_t size() noexcept { return sizeof...(Ints); }
};
// index_sequence
//
// A helper template for an `integer_sequence` of `size_t`,
// `absl::index_sequence` is designed to be a drop-in replacement for C++14's
// `std::index_sequence`.
template <size_t... Ints>
using index_sequence = integer_sequence<size_t, Ints...>;
namespace utility_internal {
template <typename Seq, size_t SeqSize, size_t Rem>
struct Extend;
// Note that SeqSize == sizeof...(Ints). It's passed explicitly for efficiency.
template <typename T, T... Ints, size_t SeqSize>
struct Extend<integer_sequence<T, Ints...>, SeqSize, 0> {
using type = integer_sequence<T, Ints..., (Ints + SeqSize)...>;
};
template <typename T, T... Ints, size_t SeqSize>
struct Extend<integer_sequence<T, Ints...>, SeqSize, 1> {
using type = integer_sequence<T, Ints..., (Ints + SeqSize)..., 2 * SeqSize>;
};
// Recursion helper for 'make_integer_sequence<T, N>'.
// 'Gen<T, N>::type' is an alias for 'integer_sequence<T, 0, 1, ... N-1>'.
template <typename T, size_t N>
struct Gen {
using type =
typename Extend<typename Gen<T, N / 2>::type, N / 2, N % 2>::type;
};
template <typename T>
struct Gen<T, 0> {
using type = integer_sequence<T>;
};
} // namespace utility_internal
// Compile-time sequences of integers
// make_integer_sequence
//
// This template alias is equivalent to
// `integer_sequence<int, 0, 1, ..., N-1>`, and is designed to be a drop-in
// replacement for C++14's `std::make_integer_sequence`.
template <typename T, T N>
using make_integer_sequence = typename utility_internal::Gen<T, N>::type;
// make_index_sequence
//
// This template alias is equivalent to `index_sequence<0, 1, ..., N-1>`,
// and is designed to be a drop-in replacement for C++14's
// `std::make_index_sequence`.
template <size_t N>
using make_index_sequence = make_integer_sequence<size_t, N>;
// index_sequence_for
//
// Converts a typename pack into an index sequence of the same length, and
// is designed to be a drop-in replacement for C++14's
// `std::index_sequence_for()`
template <typename... Ts>
using index_sequence_for = make_index_sequence<sizeof...(Ts)>;
// Tag types
#ifdef ABSL_HAVE_STD_OPTIONAL
using std::in_place_t;
using std::in_place;
#else // ABSL_HAVE_STD_OPTIONAL
// in_place_t
//
// Tag type used to specify in-place construction, such as with
// `absl::optional`, designed to be a drop-in replacement for C++17's
// `std::in_place_t`.
struct in_place_t {};
extern const in_place_t in_place;
#endif // ABSL_HAVE_STD_OPTIONAL
#ifdef ABSL_HAVE_STD_ANY
using std::in_place_type_t;
#else
// in_place_type_t
//
// Tag type used for in-place construction when the type to construct needs to
// be specified, such as with `absl::any`, designed to be a drop-in replacement
// for C++17's `std::in_place_type_t`.
template <typename T>
struct in_place_type_t {};
#endif // ABSL_HAVE_STD_ANY
// in_place_index_t
//
// Tag type used for in-place construction when the type to construct needs to
// be specified, such as with `absl::any`, designed to be a drop-in replacement
// for C++17's `std::in_place_index_t`.
template <size_t I>
struct in_place_index_t {};
// Constexpr move and forward
// move()
//
// A constexpr version of `std::move()`, designed to be a drop-in replacement
// for C++14's `std::move()`.
template <typename T>
constexpr absl::remove_reference_t<T>&& move(T&& t) noexcept {
return static_cast<absl::remove_reference_t<T>&&>(t);
}
// forward()
//
// A constexpr version of `std::forward()`, designed to be a drop-in replacement
// for C++14's `std::forward()`.
template <typename T>
constexpr T&& forward(
absl::remove_reference_t<T>& t) noexcept { // NOLINT(runtime/references)
return static_cast<T&&>(t);
}
} // namespace absl
#endif // ABSL_UTILITY_UTILITY_H_
|
