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comparison: mfbt/Maybe.h
mfbt/Maybe.h
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- TOR_BUG_9701
- changeset 14
- 925c144e1f1f
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| -1:000000000000 | 0:ad4b26bc85b5 |
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| 1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ | |
| 2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */ | |
| 3 /* This Source Code Form is subject to the terms of the Mozilla Public | |
| 4 * License, v. 2.0. If a copy of the MPL was not distributed with this | |
| 5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | |
| 6 | |
| 7 /* A class for lazily constructing an object without sticking it on the heap. */ | |
| 8 | |
| 9 #ifndef mozilla_Maybe_h | |
| 10 #define mozilla_Maybe_h | |
| 11 | |
| 12 #include "mozilla/Alignment.h" | |
| 13 #include "mozilla/Assertions.h" | |
| 14 | |
| 15 // For placement new | |
| 16 #include <new> | |
| 17 | |
| 18 namespace mozilla { | |
| 19 | |
| 20 /* | |
| 21 * Small utility for lazily constructing objects without using dynamic storage. | |
| 22 * When a Maybe<T> is constructed, it is |empty()|, i.e., no value of T has | |
| 23 * been constructed and no T destructor will be called when the Maybe<T> is | |
| 24 * destroyed. Upon calling |construct|, a T object will be constructed with the | |
| 25 * given arguments and that object will be destroyed when the owning Maybe<T> | |
| 26 * is destroyed. | |
| 27 * | |
| 28 * N.B. GCC seems to miss some optimizations with Maybe and may generate extra | |
| 29 * branches/loads/stores. Use with caution on hot paths. | |
| 30 */ | |
| 31 template<class T> | |
| 32 class Maybe | |
| 33 { | |
| 34 AlignedStorage2<T> storage; | |
| 35 bool constructed; | |
| 36 | |
| 37 T& asT() { return *storage.addr(); } | |
| 38 | |
| 39 public: | |
| 40 Maybe() { constructed = false; } | |
| 41 ~Maybe() { if (constructed) asT().~T(); } | |
| 42 | |
| 43 bool empty() const { return !constructed; } | |
| 44 | |
| 45 void construct() { | |
| 46 MOZ_ASSERT(!constructed); | |
| 47 ::new (storage.addr()) T(); | |
| 48 constructed = true; | |
| 49 } | |
| 50 | |
| 51 template<class T1> | |
| 52 void construct(const T1& t1) { | |
| 53 MOZ_ASSERT(!constructed); | |
| 54 ::new (storage.addr()) T(t1); | |
| 55 constructed = true; | |
| 56 } | |
| 57 | |
| 58 template<class T1, class T2> | |
| 59 void construct(const T1& t1, const T2& t2) { | |
| 60 MOZ_ASSERT(!constructed); | |
| 61 ::new (storage.addr()) T(t1, t2); | |
| 62 constructed = true; | |
| 63 } | |
| 64 | |
| 65 template<class T1, class T2, class T3> | |
| 66 void construct(const T1& t1, const T2& t2, const T3& t3) { | |
| 67 MOZ_ASSERT(!constructed); | |
| 68 ::new (storage.addr()) T(t1, t2, t3); | |
| 69 constructed = true; | |
| 70 } | |
| 71 | |
| 72 template<class T1, class T2, class T3, class T4> | |
| 73 void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4) { | |
| 74 MOZ_ASSERT(!constructed); | |
| 75 ::new (storage.addr()) T(t1, t2, t3, t4); | |
| 76 constructed = true; | |
| 77 } | |
| 78 | |
| 79 template<class T1, class T2, class T3, class T4, class T5> | |
| 80 void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5) { | |
| 81 MOZ_ASSERT(!constructed); | |
| 82 ::new (storage.addr()) T(t1, t2, t3, t4, t5); | |
| 83 constructed = true; | |
| 84 } | |
| 85 | |
| 86 template<class T1, class T2, class T3, class T4, class T5, | |
| 87 class T6> | |
| 88 void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5, | |
| 89 const T6& t6) { | |
| 90 MOZ_ASSERT(!constructed); | |
| 91 ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6); | |
| 92 constructed = true; | |
| 93 } | |
| 94 | |
| 95 template<class T1, class T2, class T3, class T4, class T5, | |
| 96 class T6, class T7> | |
| 97 void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5, | |
| 98 const T6& t6, const T7& t7) { | |
| 99 MOZ_ASSERT(!constructed); | |
| 100 ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7); | |
| 101 constructed = true; | |
| 102 } | |
| 103 | |
| 104 template<class T1, class T2, class T3, class T4, class T5, | |
| 105 class T6, class T7, class T8> | |
| 106 void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5, | |
| 107 const T6& t6, const T7& t7, const T8& t8) { | |
| 108 MOZ_ASSERT(!constructed); | |
| 109 ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8); | |
| 110 constructed = true; | |
| 111 } | |
| 112 | |
| 113 template<class T1, class T2, class T3, class T4, class T5, | |
| 114 class T6, class T7, class T8, class T9> | |
| 115 void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5, | |
| 116 const T6& t6, const T7& t7, const T8& t8, const T9& t9) { | |
| 117 MOZ_ASSERT(!constructed); | |
| 118 ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8, t9); | |
| 119 constructed = true; | |
| 120 } | |
| 121 | |
| 122 template<class T1, class T2, class T3, class T4, class T5, | |
| 123 class T6, class T7, class T8, class T9, class T10> | |
| 124 void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5, | |
| 125 const T6& t6, const T7& t7, const T8& t8, const T9& t9, const T10& t10) { | |
| 126 MOZ_ASSERT(!constructed); | |
| 127 ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8, t9, t10); | |
| 128 constructed = true; | |
| 129 } | |
| 130 | |
| 131 T* addr() { | |
| 132 MOZ_ASSERT(constructed); | |
| 133 return &asT(); | |
| 134 } | |
| 135 | |
| 136 T& ref() { | |
| 137 MOZ_ASSERT(constructed); | |
| 138 return asT(); | |
| 139 } | |
| 140 | |
| 141 const T& ref() const { | |
| 142 MOZ_ASSERT(constructed); | |
| 143 return const_cast<Maybe*>(this)->asT(); | |
| 144 } | |
| 145 | |
| 146 void destroy() { | |
| 147 ref().~T(); | |
| 148 constructed = false; | |
| 149 } | |
| 150 | |
| 151 void destroyIfConstructed() { | |
| 152 if (!empty()) | |
| 153 destroy(); | |
| 154 } | |
| 155 | |
| 156 private: | |
| 157 Maybe(const Maybe& other) MOZ_DELETE; | |
| 158 const Maybe& operator=(const Maybe& other) MOZ_DELETE; | |
| 159 }; | |
| 160 | |
| 161 } // namespace mozilla | |
| 162 | |
| 163 #endif /* mozilla_Maybe_h */ |
