libstdc++-v3/include/bits/stl_construct.h

// nonstandard construct and destroy functions -*- C++ -*-

// Copyright (C) 2001-2026 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/>.

/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996,1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file bits/stl_construct.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{memory}
 */

#ifndef _STL_CONSTRUCT_H
#define _STL_CONSTRUCT_H 1

#include <new>
#include <bits/move.h>
#include <bits/stl_iterator_base_types.h> // for iterator_traits
#include <bits/stl_iterator_base_funcs.h> // for advance

/* This file provides the C++17 functions std::destroy_at, std::destroy, and
 * std::destroy_n, and the C++20 function std::construct_at.
 * It also provides std::_Construct, std::_Destroy,and std::_Destroy_n functions
 * which are defined in all standard modes and so can be used in C++98-14 code.
 * The _Destroy functions will dispatch to destroy_at during constant
 * evaluation, because calls to that function are intercepted by the compiler
 * to allow use in constant expressions.
 */

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#if __glibcxx_raw_memory_algorithms // >= C++17
  template <typename _Tp>
    _GLIBCXX20_CONSTEXPR inline void
    destroy_at(_Tp* __location)
    {
      if constexpr (__cplusplus > 201703L && is_array_v<_Tp>)
	{
	  for (auto& __x : *__location)
	    std::destroy_at(std::addressof(__x));
	}
      else
	__location->~_Tp();
    }

#if __cpp_constexpr_dynamic_alloc // >= C++20
  template<typename _Tp, typename... _Args>
    requires (!is_unbounded_array_v<_Tp>)
      && requires { ::new((void*)0) _Tp(std::declval<_Args>()...); }
    constexpr _Tp*
    construct_at(_Tp* __location, _Args&&... __args)
    noexcept(noexcept(::new((void*)0) _Tp(std::declval<_Args>()...)))
    {
      void* __loc = __location;
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 3436. std::construct_at should support arrays
      if constexpr (is_array_v<_Tp>)
	{
	  static_assert(sizeof...(_Args) == 0, "std::construct_at for array "
		       "types must not use any arguments to initialize the "
		       "array");
	  return ::new(__loc) _Tp[1]();
	}
      else
	return ::new(__loc) _Tp(std::forward<_Args>(__args)...);
    }
#endif // C++20
#endif// C++17

  /**
   * Constructs an object in existing memory by invoking an allocated
   * object's constructor with an initializer.
   */
#if __cplusplus >= 201103L
  template<typename _Tp, typename... _Args>
    _GLIBCXX20_CONSTEXPR
    inline void
    _Construct(_Tp* __p, _Args&&... __args)
    {
#if __cpp_constexpr_dynamic_alloc // >= C++20
      if (std::is_constant_evaluated())
	{
	  // Allow std::_Construct to be used in constant expressions.
	  std::construct_at(__p, std::forward<_Args>(__args)...);
	  return;
	}
#endif
      ::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...);
    }
#else
  template<typename _T1, typename _T2>
    inline void
    _Construct(_T1* __p, const _T2& __value)
    {
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 402. wrong new expression in [some_]allocator::construct
      ::new(static_cast<void*>(__p)) _T1(__value);
    }
#endif

  template<typename _T1>
    _GLIBCXX26_CONSTEXPR
    inline void
    _Construct_novalue(_T1* __p)
    { ::new(static_cast<void*>(__p)) _T1; }

  template<typename _ForwardIterator>
    _GLIBCXX20_CONSTEXPR void
    _Destroy(_ForwardIterator __first, _ForwardIterator __last);

  /**
   * Destroy the object pointed to by a pointer type.
   */
  template<typename _Tp>
    _GLIBCXX14_CONSTEXPR inline void
    _Destroy(_Tp* __pointer)
    {
#if __cpp_constexpr_dynamic_alloc // >= C++20
      std::destroy_at(__pointer);
#else
      __pointer->~_Tp();
#endif
    }

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++17-extensions" // for if-constexpr

#if __cplusplus < 201103L
  template<bool>
    struct _Destroy_aux
    {
      template<typename _ForwardIterator>
	static _GLIBCXX20_CONSTEXPR void
	__destroy(_ForwardIterator __first, _ForwardIterator __last)
	{
	  for (; __first != __last; ++__first)
	    std::_Destroy(std::__addressof(*__first));
	}

      template<typename _ForwardIterator, typename _Size>
	static _GLIBCXX20_CONSTEXPR _ForwardIterator
	__destroy_n(_ForwardIterator __first, _Size __count)
	{
	  for (; __count > 0; (void)++__first, --__count)
	    std::_Destroy(std::__addressof(*__first));
	  return __first;
	}
    };

  template<>
    struct _Destroy_aux<true>
    {
      template<typename _ForwardIterator>
        static void
        __destroy(_ForwardIterator, _ForwardIterator) { }

      template<typename _ForwardIterator, typename _Size>
	static _ForwardIterator
	__destroy_n(_ForwardIterator __first, _Size __count)
	{
	  std::advance(__first, __count);
	  return __first;
	}
    };
#endif

  /**
   * Destroy a range of objects.  If the value_type of the object has
   * a trivial destructor, the compiler should optimize all of this
   * away, otherwise the objects' destructors must be invoked.
   */
  template<typename _ForwardIterator>
    _GLIBCXX20_CONSTEXPR inline void
    _Destroy(_ForwardIterator __first, _ForwardIterator __last)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
                       _Value_type;
#if __cplusplus >= 201103L
      if constexpr (!is_trivially_destructible<_Value_type>::value)
	for (; __first != __last; ++__first)
	  std::_Destroy(std::addressof(*__first));
#if __cpp_constexpr_dynamic_alloc // >= C++20
      else if (std::is_constant_evaluated())
	for (; __first != __last; ++__first)
	  std::destroy_at(std::addressof(*__first));
#endif
#else
      std::_Destroy_aux<__has_trivial_destructor(_Value_type)>::
	__destroy(__first, __last);
#endif
    }

  /**
   * Destroy a range of objects.  If the value_type of the object has
   * a trivial destructor, the compiler should optimize all of this
   * away, otherwise the objects' destructors must be invoked.
   */
  template<typename _ForwardIterator, typename _Size>
    _GLIBCXX20_CONSTEXPR inline _ForwardIterator
    _Destroy_n(_ForwardIterator __first, _Size __count)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
                       _Value_type;
#if __cplusplus >= 201103L
      if constexpr (!is_trivially_destructible<_Value_type>::value)
	for (; __count > 0; (void)++__first, --__count)
	  std::_Destroy(std::addressof(*__first));
#if __cpp_constexpr_dynamic_alloc // >= C++20
      else if (std::is_constant_evaluated())
	for (; __count > 0; (void)++__first, --__count)
	  std::destroy_at(std::addressof(*__first));
#endif
      else
	std::advance(__first, __count);
      return __first;
#else
      return std::_Destroy_aux<__has_trivial_destructor(_Value_type)>::
	__destroy_n(__first, __count);
#endif
    }
#pragma GCC diagnostic pop

#if __glibcxx_raw_memory_algorithms // >= C++17
  template <typename _ForwardIterator>
    _GLIBCXX20_CONSTEXPR inline void
    destroy(_ForwardIterator __first, _ForwardIterator __last)
    {
      std::_Destroy(__first, __last);
    }

  template <typename _ForwardIterator, typename _Size>
    _GLIBCXX20_CONSTEXPR inline _ForwardIterator
    destroy_n(_ForwardIterator __first, _Size __count)
    {
      return std::_Destroy_n(__first, __count);
    }
#endif // C++17

#if __glibcxx_start_lifetime_as >= 202207L // C++ >= 23
  template<typename _Tp>
    [[__gnu__::__always_inline__]]
    inline _Tp*
    start_lifetime_as(void* __p) noexcept
    {
#if __glibcxx_is_implicit_lifetime >= 202302L
      static_assert(is_implicit_lifetime_v<_Tp>);
#endif
      auto __q = reinterpret_cast<_Tp*>(__p);
      __asm__ __volatile__("" : "=g" (__q), "=m" (*__q)
			   : "0" (__q), "m" (*__q));
      return __q;
    }

  template<typename _Tp>
    [[__gnu__::__always_inline__]]
    inline const _Tp*
    start_lifetime_as(const void* __p) noexcept
    {
#if __glibcxx_is_implicit_lifetime >= 202302L
      static_assert(is_implicit_lifetime_v<_Tp>);
#endif
      auto __q = reinterpret_cast<const _Tp*>(__p);
      auto __r = reinterpret_cast<_Tp*>(const_cast<void*>(__p));
      __asm__ __volatile__("" : "=g" (__q), "=m" (*__r)
			   : "0" (__q), "m" (*__q));
      return __q;
    }

  template<typename _Tp>
    [[__gnu__::__always_inline__]]
    inline volatile _Tp*
    start_lifetime_as(volatile void* __p) noexcept
    {
#if __glibcxx_is_implicit_lifetime >= 202302L
      static_assert(is_implicit_lifetime_v<_Tp>);
#endif
      auto __q = reinterpret_cast<volatile _Tp*>(__p);
      auto __r = reinterpret_cast<_Tp*>(const_cast<void*>(__p));
      __asm__ __volatile__("" : "=g" (__q), "=m" (*__r)
			   : "0" (__q), "m" (*__q));
      return __q;
    }

  template<typename _Tp>
    [[__gnu__::__always_inline__]]
    inline const volatile _Tp*
    start_lifetime_as(const volatile void* __p) noexcept
    {
#if __glibcxx_is_implicit_lifetime >= 202302L
      static_assert(is_implicit_lifetime_v<_Tp>);
#endif
      auto __q = reinterpret_cast<const volatile _Tp*>(__p);
      auto __r = reinterpret_cast<_Tp*>(const_cast<void*>(__p));
      __asm__ __volatile__("" : "=g" (__q), "=m" (*__r)
			   : "0" (__q), "m" (*__q));
      return __q;
    }

  template<typename _Tp>
    [[__gnu__::__always_inline__]]
    inline _Tp*
    start_lifetime_as_array(void* __p, size_t __n) noexcept
    {
      static_assert(sizeof(_Tp), "template argument must be a complete type");

      auto __q = reinterpret_cast<_Tp*>(__p);
      if (!__n)
	return __q;
      auto __r = (__extension__ reinterpret_cast<_Tp(*)[__n]>(__p));
      __asm__ __volatile__("" : "=g" (__q), "=m" (*__r)
			   : "0" (__q), "m" (*__r));
      return __q;
    }

  template<typename _Tp>
    [[__gnu__::__always_inline__]]
    inline const _Tp*
    start_lifetime_as_array(const void* __p, size_t __n) noexcept
    {
      static_assert(sizeof(_Tp), "template argument must be a complete type");

      auto __q = reinterpret_cast<const _Tp*>(__p);
      if (!__n)
	return __q;
      auto __r = (__extension__ reinterpret_cast<const _Tp(*)[__n]>(__p));
      auto __s = (__extension__
		  reinterpret_cast<_Tp(*)[__n]>(const_cast<void*>(__p)));
      __asm__ __volatile__("" : "=g" (__q), "=m" (*__s)
			   : "0" (__q), "m" (*__r));
      return __q;
    }

  template<typename _Tp>
    [[__gnu__::__always_inline__]]
    inline volatile _Tp*
    start_lifetime_as_array(volatile void* __p, size_t __n) noexcept
    {
      static_assert(sizeof(_Tp), "template argument must be a complete type");

      auto __q = reinterpret_cast<volatile _Tp*>(__p);
      if (!__n)
	return __q;
      auto __r = (__extension__ reinterpret_cast<volatile _Tp(*)[__n]>(__p));
      auto __s = (__extension__
		  reinterpret_cast<_Tp(*)[__n]>(const_cast<void*>(__p)));
      __asm__ __volatile__("" : "=g" (__q), "=m" (*__s)
			   : "0" (__q), "m" (*__r));
      return __q;
    }

  template<typename _Tp>
    [[__gnu__::__always_inline__]]
    inline const volatile _Tp*
    start_lifetime_as_array(const volatile void* __p, size_t __n) noexcept
    {
      static_assert(sizeof(_Tp), "template argument must be a complete type");

      auto __q = reinterpret_cast<const volatile _Tp*>(__p);
      if (!__n)
	return __q;
      auto __r = (__extension__ reinterpret_cast<const volatile _Tp(*)[__n]>(__p));
      auto __s = (__extension__
		  reinterpret_cast<_Tp(*)[__n]>(const_cast<void*>(__p)));
      __asm__ __volatile__("" : "=g" (__q), "=m" (*__s)
			   : "0" (__q), "m" (*__r));
      return __q;
    }
#endif // C++23

#if __glibcxx_start_lifetime >= 202603L // C++ >= 26
  template <typename _Tp>
    constexpr void
    start_lifetime(_Tp& __r) noexcept
    {
#ifdef __cpp_lib_is_implicit_lifetime
      static_assert(std::is_implicit_lifetime_v<_Tp>);
#endif
#ifdef __cpp_lib_is_aggregate
      static_assert(std::is_aggregate_v<_Tp>);
#endif
      __builtin_start_lifetime(__builtin_addressof(__r));
    }
#endif // C++26

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif /* _STL_CONSTRUCT_H */