/* Copyright (C) 2017-2024 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 GDBSUPPORT_DEFAULT_INIT_ALLOC_H
#define GDBSUPPORT_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 /* GDBSUPPORT_DEFAULT_INIT_ALLOC_H */