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✏️ Editing: tuple

// <tuple> -*- C++ -*-

// Copyright (C) 2007-2021 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library 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, or (at your option)
// any later version.

// This library 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.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file include/tuple
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_TUPLE
#define _GLIBCXX_TUPLE 1

#pragma GCC system_header

#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else

#include <utility>
#include <array>
#include <bits/uses_allocator.h>
#include <bits/invoke.h>
#if __cplusplus > 201703L
# include <compare>
# define __cpp_lib_constexpr_tuple 201811L
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

/**
   *  @addtogroup utilities
   *  @{
   */

template<typename... _Elements>
    class tuple;

template<typename _Tp>
    struct __is_empty_non_tuple : is_empty<_Tp> { };

// Using EBO for elements that are tuples causes ambiguous base errors.
  template<typename _El0, typename... _El>
    struct __is_empty_non_tuple<tuple<_El0, _El...>> : false_type { };

// Use the Empty Base-class Optimization for empty, non-final types.
  template<typename _Tp>
    using __empty_not_final
    = typename conditional<__is_final(_Tp), false_type,
			   __is_empty_non_tuple<_Tp>>::type;

template<size_t _Idx, typename _Head,
	   bool = __empty_not_final<_Head>::value>
    struct _Head_base;

#if __has_cpp_attribute(__no_unique_address__)
  template<size_t _Idx, typename _Head>
    struct _Head_base<_Idx, _Head, true>
    {
      constexpr _Head_base()
      : _M_head_impl() { }

constexpr _Head_base(const _Head& __h)
      : _M_head_impl(__h) { }

constexpr _Head_base(const _Head_base&) = default;
      constexpr _Head_base(_Head_base&&) = default;

template<typename _UHead>
	constexpr _Head_base(_UHead&& __h)
	: _M_head_impl(std::forward<_UHead>(__h)) { }

_GLIBCXX20_CONSTEXPR
      _Head_base(allocator_arg_t, __uses_alloc0)
      : _M_head_impl() { }

template<typename _Alloc>
	_GLIBCXX20_CONSTEXPR
	_Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
	: _M_head_impl(allocator_arg, *__a._M_a) { }

template<typename _Alloc>
	_GLIBCXX20_CONSTEXPR
	_Head_base(allocator_arg_t, __uses_alloc2<_Alloc> __a)
	: _M_head_impl(*__a._M_a) { }

template<typename _UHead>
	_GLIBCXX20_CONSTEXPR
	_Head_base(__uses_alloc0, _UHead&& __uhead)
	: _M_head_impl(std::forward<_UHead>(__uhead)) { }

template<typename _Alloc, typename _UHead>
	_GLIBCXX20_CONSTEXPR
	_Head_base(__uses_alloc1<_Alloc> __a, _UHead&& __uhead)
	: _M_head_impl(allocator_arg, *__a._M_a, std::forward<_UHead>(__uhead))
	{ }

template<typename _Alloc, typename _UHead>
	_GLIBCXX20_CONSTEXPR
	_Head_base(__uses_alloc2<_Alloc> __a, _UHead&& __uhead)
	: _M_head_impl(std::forward<_UHead>(__uhead), *__a._M_a) { }

static constexpr _Head&
      _M_head(_Head_base& __b) noexcept { return __b._M_head_impl; }

static constexpr const _Head&
      _M_head(const _Head_base& __b) noexcept { return __b._M_head_impl; }

[[__no_unique_address__]] _Head _M_head_impl;
    };
#else
  template<size_t _Idx, typename _Head>
    struct _Head_base<_Idx, _Head, true>
    : public _Head
    {
      constexpr _Head_base()
      : _Head() { }

constexpr _Head_base(const _Head& __h)
      : _Head(__h) { }

constexpr _Head_base(const _Head_base&) = default;
      constexpr _Head_base(_Head_base&&) = default;

template<typename _UHead>
        constexpr _Head_base(_UHead&& __h)
	: _Head(std::forward<_UHead>(__h)) { }

_GLIBCXX20_CONSTEXPR
      _Head_base(allocator_arg_t, __uses_alloc0)
      : _Head() { }

template<typename _Alloc>
	_GLIBCXX20_CONSTEXPR
	_Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)
	: _Head(allocator_arg, *__a._M_a) { }

template<typename _Alloc>
	_GLIBCXX20_CONSTEXPR
	_Head_base(allocator_arg_t, __uses_alloc2<_Alloc> __a)
	: _Head(*__a._M_a) { }

template<typename _UHead>
	_GLIBCXX20_CONSTEXPR
	_Head_base(__uses_alloc0, _UHead&& __uhead)
	: _Head(std::forward<_UHead>(__uhead)) { }

template<typename _Alloc, typename _UHead>
	_GLIBCXX20_CONSTEXPR
	_Head_base(__uses_alloc1<_Alloc> __a, _UHead&& __uhead)
	: _Head(allocator_arg, *__a._M_a, std::forward<_UHead>(__uhead)) { }

template<typename _Alloc, typename _UHead>
	_GLIBCXX20_CONSTEXPR
	_Head_base(__uses_alloc2<_Alloc> __a, _UHead&& __uhead)
	: _Head(std::forward<_UHead>(__uhead), *__a._M_a) { }

static constexpr _Head&
      _M_head(_Head_base& __b) noexcept { return __b; }

static constexpr const _Head&
      _M_head(const _Head_base& __b) noexcept { return __b; }
    };
#endif

template<size_t _Idx, typename _Head>
    struct _Head_base<_Idx, _Head, false>
    {
      constexpr _Head_base()
      : _M_head_impl() { }

constexpr _Head_base(const _Head& __h)
      : _M_head_impl(__h) { }

constexpr _Head_base(const _Head_base&) = default;
      constexpr _Head_base(_Head_base&&) = default;

template<typename _UHead>
        constexpr _Head_base(_UHead&& __h)
	: _M_head_impl(std::forward<_UHead>(__h)) { }