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default-init-alloc.h
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1 /* Copyright (C) 2017-2018 Free Software Foundation, Inc.
2
3 This file is part of GDB.
4
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
17
18 #ifndef COMMON_DEFAULT_INIT_ALLOC_H
19 #define COMMON_DEFAULT_INIT_ALLOC_H
20
21 namespace gdb {
22
23 /* An allocator that default constructs using default-initialization
24 rather than value-initialization. The idea is to use this when you
25 don't want to default construct elements of containers of trivial
26 types using zero-initialization. */
27
28 /* Mostly as implementation convenience, this is implemented as an
29 adapter that given an allocator A, overrides 'A::construct()'. 'A'
30 defaults to std::allocator<T>. */
31
32 template<typename T, typename A = std::allocator<T>>
33 class default_init_allocator : public A
34 {
35 public:
36 /* Pull in A's ctors. */
37 using A::A;
38
39 /* Override rebind. */
40 template<typename U>
41 struct rebind
42 {
43 /* A couple helpers just to make it a bit more readable. */
44 typedef std::allocator_traits<A> traits_;
45 typedef typename traits_::template rebind_alloc<U> alloc_;
46
47 /* This is what we're after. */
48 typedef default_init_allocator<U, alloc_> other;
49 };
50
51 /* Make the base allocator's construct method(s) visible. */
52 using A::construct;
53
54 /* .. and provide an override/overload for the case of default
55 construction (i.e., no arguments). This is where we construct
56 with default-init. */
57 template <typename U>
58 void construct (U *ptr)
59 noexcept (std::is_nothrow_default_constructible<U>::value)
60 {
61 ::new ((void *) ptr) U; /* default-init */
62 }
63 };
64
65 } /* namespace gdb */
66
67 #endif /* COMMON_DEFAULT_INIT_ALLOC_H */
gdb::default_init_allocator
Definition: default-init-alloc.h:33
gdb::default_init_allocator::rebind::other
default_init_allocator< U, alloc_ > other
Definition: default-init-alloc.h:48
gdb::default_init_allocator::rebind::alloc_
traits_::template rebind_alloc< U > alloc_
Definition: default-init-alloc.h:45
gdb::default_init_allocator::rebind
Definition: default-init-alloc.h:41
gdb
Definition: array-view.h:66
gdb::default_init_allocator::rebind::traits_
std::allocator_traits< A > traits_
Definition: default-init-alloc.h:44
A
Definition: ia64-tdep.c:79
gdb::default_init_allocator::construct
void construct(U *ptr) noexcept(std::is_nothrow_default_constructible< U >::value)
Definition: default-init-alloc.h:58