1/* Copyright (C) 2017-2020 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
21namespace 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
32template<typename T, typename A = std::allocator<T>>
33class default_init_allocator : public A
34{
35public:
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 */
68