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
|
/* An optional object.
Copyright (C) 2017-2023 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef COMMON_GDB_OPTIONAL_H
#define COMMON_GDB_OPTIONAL_H
#include "gdbsupport/traits.h"
namespace gdb
{
struct in_place_t
{
explicit in_place_t () = default;
};
constexpr gdb::in_place_t in_place {};
/* This class attempts to be a compatible subset of std::optional,
which is slated to be available in C++17. This class optionally
holds an object of some type -- by default it is constructed not
holding an object, but later the object can be "emplaced". This is
similar to using std::unique_ptr, but in-object allocation is
guaranteed.
Unlike std::optional, we currently only support copy/move
construction/assignment of an optional<T> from either exactly
optional<T> or T. I.e., we don't support copy/move
construction/assignment from optional<U> or U, when U is a type
convertible to T. Making that work depending on the definitions of
T and U is somewhat complicated, and currently the users of this
class don't need it. */
template<typename T>
class optional
{
public:
constexpr optional ()
: m_dummy ()
{}
template<typename... Args>
constexpr optional (in_place_t, Args &&... args)
: m_item (std::forward<Args> (args)...),
m_instantiated (true)
{}
~optional ()
{ this->reset (); }
/* Copy and move constructors. */
optional (const optional &other)
{
if (other.m_instantiated)
this->emplace (other.get ());
}
optional (optional &&other)
noexcept(std::is_nothrow_move_constructible<T> ())
{
if (other.m_instantiated)
this->emplace (std::move (other.get ()));
}
constexpr optional (const T &other)
: m_item (other),
m_instantiated (true)
{}
constexpr optional (T &&other)
noexcept (std::is_nothrow_move_constructible<T> ())
: m_item (std::move (other)),
m_instantiated (true)
{}
/* Assignment operators. */
optional &
operator= (const optional &other)
{
if (m_instantiated && other.m_instantiated)
this->get () = other.get ();
else
{
if (other.m_instantiated)
this->emplace (other.get ());
else
this->reset ();
}
return *this;
}
optional &
operator= (optional &&other)
noexcept (And<std::is_nothrow_move_constructible<T>,
std::is_nothrow_move_assignable<T>> ())
{
if (m_instantiated && other.m_instantiated)
this->get () = std::move (other.get ());
else
{
if (other.m_instantiated)
this->emplace (std::move (other.get ()));
else
this->reset ();
}
return *this;
}
optional &
operator= (const T &other)
{
if (m_instantiated)
this->get () = other;
else
this->emplace (other);
return *this;
}
optional &
operator= (T &&other)
noexcept (And<std::is_nothrow_move_constructible<T>,
std::is_nothrow_move_assignable<T>> ())
{
if (m_instantiated)
this->get () = std::move (other);
else
this->emplace (std::move (other));
return *this;
}
template<typename... Args>
T &emplace (Args &&... args)
{
this->reset ();
new (&m_item) T (std::forward<Args>(args)...);
m_instantiated = true;
return this->get ();
}
/* Observers. */
constexpr const T *operator-> () const
{ return std::addressof (this->get ()); }
T *operator-> ()
{ return std::addressof (this->get ()); }
constexpr const T &operator* () const &
{ return this->get (); }
T &operator* () &
{ return this->get (); }
T &&operator* () &&
{ return std::move (this->get ()); }
constexpr const T &&operator* () const &&
{ return std::move (this->get ()); }
constexpr explicit operator bool () const noexcept
{ return m_instantiated; }
constexpr bool has_value () const noexcept
{ return m_instantiated; }
/* 'reset' is a 'safe' operation with no precondition. */
void reset () noexcept
{
if (m_instantiated)
this->destroy ();
}
private:
/* Destroy the object. */
void destroy ()
{
gdb_assert (m_instantiated);
m_instantiated = false;
m_item.~T ();
}
/* The get operations have m_instantiated as a precondition. */
T &get () noexcept
{
#if defined(_GLIBCXX_DEBUG) && __cplusplus >= 201402L
gdb_assert (this->has_value ());
#endif
return m_item;
}
constexpr const T &get () const noexcept
{
#if defined(_GLIBCXX_DEBUG) && __cplusplus >= 201402L
gdb_assert (this->has_value ());
#endif
return m_item;
}
/* The object. */
union
{
struct { } m_dummy;
T m_item;
volatile char dont_use; /* Silences -Wmaybe-uninitialized warning, see
PR gcc/80635. */
};
/* True if the object was ever emplaced. */
bool m_instantiated = false;
};
}
#endif /* COMMON_GDB_OPTIONAL_H */
|
