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/* 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_DEFAULT_INIT_ALLOC_H
#define COMMON_DEFAULT_INIT_ALLOC_H
#if __cplusplus >= 202002L
#include <memory_resource>
#endif
namespace gdb {
/* An allocator that default constructs using default-initialization
rather than value-initialization. The idea is to use this when you
don't want to default construct elements of containers of trivial
types using zero-initialization. */
/* Mostly as implementation convenience, this is implemented as an
adapter that given an allocator A, overrides 'A::construct()'. 'A'
defaults to std::allocator<T>. */
template<typename T,
typename A
#if __cplusplus >= 202002L
= std::pmr::polymorphic_allocator<T>
#else
= std::allocator<T>
#endif
>
class default_init_allocator : public A
{
public:
/* Pull in A's ctors. */
using A::A;
/* Override rebind. */
template<typename U>
struct rebind
{
/* A couple helpers just to make it a bit more readable. */
typedef std::allocator_traits<A> traits_;
typedef typename traits_::template rebind_alloc<U> alloc_;
/* This is what we're after. */
typedef default_init_allocator<U, alloc_> other;
};
/* Make the base allocator's construct method(s) visible. */
using A::construct;
/* .. and provide an override/overload for the case of default
construction (i.e., no arguments). This is where we construct
with default-init. */
template <typename U>
void construct (U *ptr)
noexcept (std::is_nothrow_default_constructible<U>::value)
{
::new ((void *) ptr) U; /* default-init */
}
};
} /* namespace gdb */
#endif /* COMMON_DEFAULT_INIT_ALLOC_H */
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