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
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
|
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* A class holding a pair of objects that tries to conserve storage space. */
#ifndef mozilla_CompactPair_h
#define mozilla_CompactPair_h
#include <type_traits>
#include <tuple>
#include <utility>
#include "mozilla/Attributes.h"
namespace mozilla {
namespace detail {
enum StorageType { AsBase, AsMember };
// Optimize storage using the Empty Base Optimization -- that empty base classes
// don't take up space -- to optimize size when one or the other class is
// stateless and can be used as a base class.
//
// The extra conditions on storage for B are necessary so that CompactPairHelper
// won't ambiguously inherit from either A or B, such that one or the other base
// class would be inaccessible.
template <typename A, typename B,
detail::StorageType =
std::is_empty_v<A> ? detail::AsBase : detail::AsMember,
detail::StorageType = std::is_empty_v<B> &&
!std::is_base_of<A, B>::value &&
!std::is_base_of<B, A>::value
? detail::AsBase
: detail::AsMember>
struct CompactPairHelper;
template <typename A, typename B>
struct CompactPairHelper<A, B, AsMember, AsMember> {
protected:
template <typename... AArgs, std::size_t... AIndexes, typename... BArgs,
std::size_t... BIndexes>
constexpr CompactPairHelper(std::tuple<AArgs...>& aATuple,
std::tuple<BArgs...>& aBTuple,
std::index_sequence<AIndexes...>,
std::index_sequence<BIndexes...>)
: mFirstA(std::forward<AArgs>(std::get<AIndexes>(aATuple))...),
mSecondB(std::forward<BArgs>(std::get<BIndexes>(aBTuple))...) {}
public:
template <typename AArg, typename BArg>
constexpr CompactPairHelper(AArg&& aA, BArg&& aB)
: mFirstA(std::forward<AArg>(aA)), mSecondB(std::forward<BArg>(aB)) {}
constexpr A& first() { return mFirstA; }
constexpr const A& first() const { return mFirstA; }
constexpr B& second() { return mSecondB; }
constexpr const B& second() const { return mSecondB; }
void swap(CompactPairHelper& aOther) {
std::swap(mFirstA, aOther.mFirstA);
std::swap(mSecondB, aOther.mSecondB);
}
private:
A mFirstA;
B mSecondB;
};
template <typename A, typename B>
struct CompactPairHelper<A, B, AsMember, AsBase> : private B {
protected:
template <typename... AArgs, std::size_t... AIndexes, typename... BArgs,
std::size_t... BIndexes>
constexpr CompactPairHelper(std::tuple<AArgs...>& aATuple,
std::tuple<BArgs...>& aBTuple,
std::index_sequence<AIndexes...>,
std::index_sequence<BIndexes...>)
: B(std::forward<BArgs>(std::get<BIndexes>(aBTuple))...),
mFirstA(std::forward<AArgs>(std::get<AIndexes>(aATuple))...) {}
public:
template <typename AArg, typename BArg>
constexpr CompactPairHelper(AArg&& aA, BArg&& aB)
: B(std::forward<BArg>(aB)), mFirstA(std::forward<AArg>(aA)) {}
constexpr A& first() { return mFirstA; }
constexpr const A& first() const { return mFirstA; }
constexpr B& second() { return *this; }
constexpr const B& second() const { return *this; }
void swap(CompactPairHelper& aOther) {
std::swap(mFirstA, aOther.mFirstA);
std::swap(static_cast<B&>(*this), static_cast<B&>(aOther));
}
private:
A mFirstA;
};
template <typename A, typename B>
struct CompactPairHelper<A, B, AsBase, AsMember> : private A {
protected:
template <typename... AArgs, std::size_t... AIndexes, typename... BArgs,
std::size_t... BIndexes>
constexpr CompactPairHelper(std::tuple<AArgs...>& aATuple,
std::tuple<BArgs...>& aBTuple,
std::index_sequence<AIndexes...>,
std::index_sequence<BIndexes...>)
: A(std::forward<AArgs>(std::get<AIndexes>(aATuple))...),
mSecondB(std::forward<BArgs>(std::get<BIndexes>(aBTuple))...) {}
public:
template <typename AArg, typename BArg>
constexpr CompactPairHelper(AArg&& aA, BArg&& aB)
: A(std::forward<AArg>(aA)), mSecondB(std::forward<BArg>(aB)) {}
constexpr A& first() { return *this; }
constexpr const A& first() const { return *this; }
constexpr B& second() { return mSecondB; }
constexpr const B& second() const { return mSecondB; }
void swap(CompactPairHelper& aOther) {
std::swap(static_cast<A&>(*this), static_cast<A&>(aOther));
std::swap(mSecondB, aOther.mSecondB);
}
private:
B mSecondB;
};
template <typename A, typename B>
struct CompactPairHelper<A, B, AsBase, AsBase> : private A, private B {
protected:
template <typename... AArgs, std::size_t... AIndexes, typename... BArgs,
std::size_t... BIndexes>
constexpr CompactPairHelper(std::tuple<AArgs...>& aATuple,
std::tuple<BArgs...>& aBTuple,
std::index_sequence<AIndexes...>,
std::index_sequence<BIndexes...>)
: A(std::forward<AArgs>(std::get<AIndexes>(aATuple))...),
B(std::forward<BArgs>(std::get<BIndexes>(aBTuple))...) {}
public:
template <typename AArg, typename BArg>
constexpr CompactPairHelper(AArg&& aA, BArg&& aB)
: A(std::forward<AArg>(aA)), B(std::forward<BArg>(aB)) {}
constexpr A& first() { return static_cast<A&>(*this); }
constexpr const A& first() const { return static_cast<A&>(*this); }
constexpr B& second() { return static_cast<B&>(*this); }
constexpr const B& second() const { return static_cast<B&>(*this); }
void swap(CompactPairHelper& aOther) {
std::swap(static_cast<A&>(*this), static_cast<A&>(aOther));
std::swap(static_cast<B&>(*this), static_cast<B&>(aOther));
}
};
} // namespace detail
/**
* CompactPair is the logical concatenation of an instance of A with an instance
* B. Space is conserved when possible. Neither A nor B may be a final class.
*
* In general if space conservation is not critical is preferred to use
* std::pair.
*
* It's typically clearer to have individual A and B member fields. Except if
* you want the space-conserving qualities of CompactPair, you're probably
* better off not using this!
*
* No guarantees are provided about the memory layout of A and B, the order of
* initialization or destruction of A and B, and so on. (This is approximately
* required to optimize space usage.) The first/second names are merely
* conceptual!
*/
template <typename A, typename B>
struct CompactPair : private detail::CompactPairHelper<A, B> {
typedef typename detail::CompactPairHelper<A, B> Base;
using Base::Base;
template <typename... AArgs, typename... BArgs>
constexpr CompactPair(std::piecewise_construct_t, std::tuple<AArgs...> aFirst,
std::tuple<BArgs...> aSecond)
: Base(aFirst, aSecond, std::index_sequence_for<AArgs...>(),
std::index_sequence_for<BArgs...>()) {}
CompactPair(CompactPair&& aOther) = default;
CompactPair(const CompactPair& aOther) = default;
CompactPair& operator=(CompactPair&& aOther) = default;
CompactPair& operator=(const CompactPair& aOther) = default;
/** The A instance. */
using Base::first;
/** The B instance. */
using Base::second;
/** Swap this pair with another pair. */
void swap(CompactPair& aOther) { Base::swap(aOther); }
};
/**
* MakeCompactPair allows you to construct a CompactPair instance using type
* inference. A call like this:
*
* MakeCompactPair(Foo(), Bar())
*
* will return a CompactPair<Foo, Bar>.
*/
template <typename A, typename B>
CompactPair<std::remove_cv_t<std::remove_reference_t<A>>,
std::remove_cv_t<std::remove_reference_t<B>>>
MakeCompactPair(A&& aA, B&& aB) {
return CompactPair<std::remove_cv_t<std::remove_reference_t<A>>,
std::remove_cv_t<std::remove_reference_t<B>>>(
std::forward<A>(aA), std::forward<B>(aB));
}
/**
* CompactPair equality comparison
*/
template <typename A, typename B>
bool operator==(const CompactPair<A, B>& aLhs, const CompactPair<A, B>& aRhs) {
return aLhs.first() == aRhs.first() && aLhs.second() == aRhs.second();
}
} // namespace mozilla
namespace std {
template <typename A, class B>
void swap(mozilla::CompactPair<A, B>& aX, mozilla::CompactPair<A, B>& aY) {
aX.swap(aY);
}
} // namespace std
#endif /* mozilla_CompactPair_h */
|
