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
|
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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_Pair_h
#define mozilla_Pair_h
#include "mozilla/Attributes.h"
#include "mozilla/Move.h"
#include "mozilla/TypeTraits.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 PairHelper 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 =
IsEmpty<A>::value ? detail::AsBase : detail::AsMember,
detail::StorageType =
IsEmpty<B>::value && !IsBaseOf<A, B>::value && !IsBaseOf<B, A>::value
? detail::AsBase
: detail::AsMember>
struct PairHelper;
template<typename A, typename B>
struct PairHelper<A, B, AsMember, AsMember>
{
protected:
template<typename AArg, typename BArg>
PairHelper(AArg&& aA, BArg&& aB)
: mFirstA(Forward<AArg>(aA)),
mSecondB(Forward<BArg>(aB))
{}
A& first() { return mFirstA; }
const A& first() const { return mFirstA; }
B& second() { return mSecondB; }
const B& second() const { return mSecondB; }
void swap(PairHelper& aOther)
{
Swap(mFirstA, aOther.mFirstA);
Swap(mSecondB, aOther.mSecondB);
}
private:
A mFirstA;
B mSecondB;
};
template<typename A, typename B>
struct PairHelper<A, B, AsMember, AsBase> : private B
{
protected:
template<typename AArg, typename BArg>
PairHelper(AArg&& aA, BArg&& aB)
: B(Forward<BArg>(aB)),
mFirstA(Forward<AArg>(aA))
{}
A& first() { return mFirstA; }
const A& first() const { return mFirstA; }
B& second() { return *this; }
const B& second() const { return *this; }
void swap(PairHelper& aOther)
{
Swap(mFirstA, aOther.mFirstA);
Swap(static_cast<B&>(*this), static_cast<B&>(aOther));
}
private:
A mFirstA;
};
template<typename A, typename B>
struct PairHelper<A, B, AsBase, AsMember> : private A
{
protected:
template<typename AArg, typename BArg>
PairHelper(AArg&& aA, BArg&& aB)
: A(Forward<AArg>(aA)),
mSecondB(Forward<BArg>(aB))
{}
A& first() { return *this; }
const A& first() const { return *this; }
B& second() { return mSecondB; }
const B& second() const { return mSecondB; }
void swap(PairHelper& aOther)
{
Swap(static_cast<A&>(*this), static_cast<A&>(aOther));
Swap(mSecondB, aOther.mSecondB);
}
private:
B mSecondB;
};
template<typename A, typename B>
struct PairHelper<A, B, AsBase, AsBase> : private A, private B
{
protected:
template<typename AArg, typename BArg>
PairHelper(AArg&& aA, BArg&& aB)
: A(Forward<AArg>(aA)),
B(Forward<BArg>(aB))
{}
A& first() { return static_cast<A&>(*this); }
const A& first() const { return static_cast<A&>(*this); }
B& second() { return static_cast<B&>(*this); }
const B& second() const { return static_cast<B&>(*this); }
void swap(PairHelper& aOther)
{
Swap(static_cast<A&>(*this), static_cast<A&>(aOther));
Swap(static_cast<B&>(*this), static_cast<B&>(aOther));
}
};
} // namespace detail
/**
* Pair 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.
*
* It's typically clearer to have individual A and B member fields. Except if
* you want the space-conserving qualities of Pair, 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 Pair
: private detail::PairHelper<A, B>
{
typedef typename detail::PairHelper<A, B> Base;
public:
template<typename AArg, typename BArg>
Pair(AArg&& aA, BArg&& aB)
: Base(Forward<AArg>(aA), Forward<BArg>(aB))
{}
Pair(Pair&& aOther)
: Base(Move(aOther.first()), Move(aOther.second()))
{ }
Pair(const Pair& aOther) = default;
Pair& operator=(Pair&& aOther)
{
MOZ_ASSERT(this != &aOther, "Self-moves are prohibited");
first() = Move(aOther.first());
second() = Move(aOther.second());
return *this;
}
Pair& operator=(const Pair& aOther) = default;
/** The A instance. */
using Base::first;
/** The B instance. */
using Base::second;
/** Swap this pair with another pair. */
void swap(Pair& aOther) { Base::swap(aOther); }
};
template<typename A, class B>
void
Swap(Pair<A, B>& aX, Pair<A, B>& aY)
{
aX.swap(aY);
}
/**
* MakePair allows you to construct a Pair instance using type inference. A call
* like this:
*
* MakePair(Foo(), Bar())
*
* will return a Pair<Foo, Bar>.
*/
template<typename A, typename B>
Pair<typename RemoveCV<typename RemoveReference<A>::Type>::Type,
typename RemoveCV<typename RemoveReference<B>::Type>::Type>
MakePair(A&& aA, B&& aB)
{
return
Pair<typename RemoveCV<typename RemoveReference<A>::Type>::Type,
typename RemoveCV<typename RemoveReference<B>::Type>::Type>(
Forward<A>(aA),
Forward<B>(aB));
}
} // namespace mozilla
#endif /* mozilla_Pair_h */
|
