/src/LPM/external.protobuf/include/google/protobuf/explicitly_constructed.h
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1 | | // Protocol Buffers - Google's data interchange format |
2 | | // Copyright 2008 Google Inc. All rights reserved. |
3 | | // https://developers.google.com/protocol-buffers/ |
4 | | // |
5 | | // Redistribution and use in source and binary forms, with or without |
6 | | // modification, are permitted provided that the following conditions are |
7 | | // met: |
8 | | // |
9 | | // * Redistributions of source code must retain the above copyright |
10 | | // notice, this list of conditions and the following disclaimer. |
11 | | // * Redistributions in binary form must reproduce the above |
12 | | // copyright notice, this list of conditions and the following disclaimer |
13 | | // in the documentation and/or other materials provided with the |
14 | | // distribution. |
15 | | // * Neither the name of Google Inc. nor the names of its |
16 | | // contributors may be used to endorse or promote products derived from |
17 | | // this software without specific prior written permission. |
18 | | // |
19 | | // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
20 | | // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
21 | | // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
22 | | // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
23 | | // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
24 | | // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
25 | | // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
26 | | // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
27 | | // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
28 | | // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
29 | | // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
30 | | |
31 | | #ifndef GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__ |
32 | | #define GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__ |
33 | | |
34 | | #include <stdint.h> |
35 | | |
36 | | #include <string> |
37 | | #include <utility> |
38 | | |
39 | | // clang-format off |
40 | | #include "google/protobuf/port_def.inc" |
41 | | // clang-format on |
42 | | |
43 | | namespace google { |
44 | | namespace protobuf { |
45 | | namespace internal { |
46 | | |
47 | | // Wraps a variable whose constructor and destructor are explicitly |
48 | | // called. It is particularly useful for a global variable, without its |
49 | | // constructor and destructor run on start and end of the program lifetime. |
50 | | // This circumvents the initial construction order fiasco, while keeping |
51 | | // the address of the empty string a compile time constant. |
52 | | // |
53 | | // Pay special attention to the initialization state of the object. |
54 | | // 1. The object is "uninitialized" to begin with. |
55 | | // 2. Call Construct() or DefaultConstruct() only if the object is |
56 | | // uninitialized. After the call, the object becomes "initialized". |
57 | | // 3. Call get() and get_mutable() only if the object is initialized. |
58 | | // 4. Call Destruct() only if the object is initialized. |
59 | | // After the call, the object becomes uninitialized. |
60 | | template <typename T, size_t min_align = 1> |
61 | | class ExplicitlyConstructed { |
62 | | public: |
63 | | void DefaultConstruct() { new (&union_) T(); } |
64 | | |
65 | | template <typename... Args> |
66 | | void Construct(Args&&... args) { |
67 | | new (&union_) T(std::forward<Args>(args)...); |
68 | | } |
69 | | |
70 | | void Destruct() { get_mutable()->~T(); } |
71 | | |
72 | 0 | constexpr const T& get() const { return reinterpret_cast<const T&>(union_); } |
73 | | T* get_mutable() { return reinterpret_cast<T*>(&union_); } |
74 | | |
75 | | private: |
76 | | union AlignedUnion { |
77 | | alignas(min_align > alignof(T) ? min_align |
78 | | : alignof(T)) char space[sizeof(T)]; |
79 | | int64_t align_to_int64; |
80 | | void* align_to_ptr; |
81 | | } union_; |
82 | | }; |
83 | | |
84 | | // ArenaStringPtr compatible explicitly constructed string type. |
85 | | // This empty string type is aligned with a minimum alignment of 8 bytes |
86 | | // which is the minimum requirement of ArenaStringPtr |
87 | | using ExplicitlyConstructedArenaString = ExplicitlyConstructed<std::string, 8>; |
88 | | |
89 | | } // namespace internal |
90 | | } // namespace protobuf |
91 | | } // namespace google |
92 | | |
93 | | #include "google/protobuf/port_undef.inc" |
94 | | |
95 | | #endif // GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__ |