unique_ptr.h

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// unique_ptr implementation -*- C++ -*-

// Copyright (C) 2008-2024 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 bits/unique_ptr.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{memory}
 */

#ifndef _UNIQUE_PTR_H
#define _UNIQUE_PTR_H 1

#include <bits/c++config.h>
#include <debug/assertions.h>
#include <type_traits>
#include <tuple>
#include <bits/stl_function.h>
#include <bits/functional_hash.h>
#if __cplusplus >= 202002L
# include <compare>
# if _GLIBCXX_HOSTED
#  include <ostream>
# endif
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   * @addtogroup pointer_abstractions
   * @{
   */

#if _GLIBCXX_USE_DEPRECATED
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
  template<typename> class auto_ptr;
#pragma GCC diagnostic pop
#endif

  /** Primary template of default_delete, used by unique_ptr for single objects
   *
   * @headerfile memory
   * @since C++11
   */
  template<typename _Tp>
    struct default_delete
    {
      /// Default constructor
      constexpr default_delete() noexcept = default;

      /** @brief Converting constructor.
       *
       * Allows conversion from a deleter for objects of another type, `_Up`,
       * only if `_Up*` is convertible to `_Tp*`.
       */
      template<typename _Up,
               typename = _Require<is_convertible<_Up*, _Tp*>>>
        _GLIBCXX23_CONSTEXPR
        default_delete(const default_delete<_Up>&) noexcept { }

      /// Calls `delete __ptr`
      _GLIBCXX23_CONSTEXPR
      void
      operator()(_Tp* __ptr) const
      {
        static_assert(!is_void<_Tp>::value,
                      "can't delete pointer to incomplete type");
        static_assert(sizeof(_Tp)>0,
                      "can't delete pointer to incomplete type");
        delete __ptr;
      }
    };

  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // DR 740 - omit specialization for array objects with a compile time length

  /** Specialization of default_delete for arrays, used by `unique_ptr<T[]>`
   *
   * @headerfile memory
   * @since C++11
   */
  template<typename _Tp>
    struct default_delete<_Tp[]>
    {
    public:
      /// Default constructor
      constexpr default_delete() noexcept = default;

      /** @brief Converting constructor.
       *
       * Allows conversion from a deleter for arrays of another type, such as
       * a const-qualified version of `_Tp`.
       *
       * Conversions from types derived from `_Tp` are not allowed because
       * it is undefined to `delete[]` an array of derived types through a
       * pointer to the base type.
       */
      template<typename _Up,
               typename = _Require<is_convertible<_Up(*)[], _Tp(*)[]>>>
        _GLIBCXX23_CONSTEXPR
        default_delete(const default_delete<_Up[]>&) noexcept { }

      /// Calls `delete[] __ptr`
      template<typename _Up>
        _GLIBCXX23_CONSTEXPR
        typename enable_if<is_convertible<_Up(*)[], _Tp(*)[]>::value>::type
        operator()(_Up* __ptr) const
        {
          static_assert(sizeof(_Tp)>0,
                        "can't delete pointer to incomplete type");
          delete [] __ptr;
        }
    };

  /// @cond undocumented

  // Manages the pointer and deleter of a unique_ptr
  template <typename _Tp, typename _Dp>
    class __uniq_ptr_impl
    {
      template <typename _Up, typename _Ep, typename = void>
        struct _Ptr
        {
          using type = _Up*;
        };

      template <typename _Up, typename _Ep>
        struct
        _Ptr<_Up, _Ep, __void_t<typename remove_reference<_Ep>::type::pointer>>
        {
          using type = typename remove_reference<_Ep>::type::pointer;
        };

    public:
      using _DeleterConstraint = enable_if<
        __and_<__not_<is_pointer<_Dp>>,
               is_default_constructible<_Dp>>::value>;

      using pointer = typename _Ptr<_Tp, _Dp>::type;

      static_assert( !is_rvalue_reference<_Dp>::value,
                     "unique_ptr's deleter type must be a function object type"
                     " or an lvalue reference type" );

      __uniq_ptr_impl() = default;
      _GLIBCXX23_CONSTEXPR
      __uniq_ptr_impl(pointer __p) : _M_t() { _M_ptr() = __p; }

      template<typename _Del>
        _GLIBCXX23_CONSTEXPR
        __uniq_ptr_impl(pointer __p, _Del&& __d)
        : _M_t(__p, std::forward<_Del>(__d)) { }

      _GLIBCXX23_CONSTEXPR
      __uniq_ptr_impl(__uniq_ptr_impl&& __u) noexcept
      : _M_t(std::move(__u._M_t))
      { __u._M_ptr() = nullptr; }

      _GLIBCXX23_CONSTEXPR
      __uniq_ptr_impl& operator=(__uniq_ptr_impl&& __u) noexcept
      {
        reset(__u.release());
        _M_deleter() = std::forward<_Dp>(__u._M_deleter());
        return *this;
      }

      _GLIBCXX23_CONSTEXPR
      pointer&   _M_ptr() noexcept { return std::get<0>(_M_t); }
      _GLIBCXX23_CONSTEXPR
      pointer    _M_ptr() const noexcept { return std::get<0>(_M_t); }
      _GLIBCXX23_CONSTEXPR
      _Dp&       _M_deleter() noexcept { return std::get<1>(_M_t); }
      _GLIBCXX23_CONSTEXPR
      const _Dp& _M_deleter() const noexcept { return std::get<1>(_M_t); }

      _GLIBCXX23_CONSTEXPR
      void reset(pointer __p) noexcept
      {
        const pointer __old_p = _M_ptr();
        _M_ptr() = __p;
        if (__old_p)
          _M_deleter()(__old_p);
      }

      _GLIBCXX23_CONSTEXPR
      pointer release() noexcept
      {
        pointer __p = _M_ptr();
        _M_ptr() = nullptr;
        return __p;
      }

      _GLIBCXX23_CONSTEXPR
      void
      swap(__uniq_ptr_impl& __rhs) noexcept
      {
        using std::swap;
        swap(this->_M_ptr(), __rhs._M_ptr());
        swap(this->_M_deleter(), __rhs._M_deleter());
      }

    private:
      tuple<pointer, _Dp> _M_t;
    };

  // Defines move construction + assignment as either defaulted or deleted.
  template <typename _Tp, typename _Dp,
            bool = is_move_constructible<_Dp>::value,
            bool = is_move_assignable<_Dp>::value>
    struct __uniq_ptr_data : __uniq_ptr_impl<_Tp, _Dp>
    {
      using __uniq_ptr_impl<_Tp, _Dp>::__uniq_ptr_impl;
      __uniq_ptr_data(__uniq_ptr_data&&) = default;
      __uniq_ptr_data& operator=(__uniq_ptr_data&&) = default;
    };

  template <typename _Tp, typename _Dp>
    struct __uniq_ptr_data<_Tp, _Dp, true, false> : __uniq_ptr_impl<_Tp, _Dp>
    {
      using __uniq_ptr_impl<_Tp, _Dp>::__uniq_ptr_impl;
      __uniq_ptr_data(__uniq_ptr_data&&) = default;
      __uniq_ptr_data& operator=(__uniq_ptr_data&&) = delete;
    };

  template <typename _Tp, typename _Dp>
    struct __uniq_ptr_data<_Tp, _Dp, false, true> : __uniq_ptr_impl<_Tp, _Dp>
    {
      using __uniq_ptr_impl<_Tp, _Dp>::__uniq_ptr_impl;
      __uniq_ptr_data(__uniq_ptr_data&&) = delete;
      __uniq_ptr_data& operator=(__uniq_ptr_data&&) = default;
    };

  template <typename _Tp, typename _Dp>
    struct __uniq_ptr_data<_Tp, _Dp, false, false> : __uniq_ptr_impl<_Tp, _Dp>
    {
      using __uniq_ptr_impl<_Tp, _Dp>::__uniq_ptr_impl;
      __uniq_ptr_data(__uniq_ptr_data&&) = delete;
      __uniq_ptr_data& operator=(__uniq_ptr_data&&) = delete;
    };
  /// @endcond

  // 20.7.1.2 unique_ptr for single objects.

  /// A move-only smart pointer that manages unique ownership of a resource.
  /// @headerfile memory
  /// @since C++11
  template <typename _Tp, typename _Dp = default_delete<_Tp>>
    class unique_ptr
    {
      template <typename _Up>
        using _DeleterConstraint =
          typename __uniq_ptr_impl<_Tp, _Up>::_DeleterConstraint::type;

      __uniq_ptr_data<_Tp, _Dp> _M_t;

    public:
      using pointer       = typename __uniq_ptr_impl<_Tp, _Dp>::pointer;
      using element_type  = _Tp;
      using deleter_type  = _Dp;

    private:
      // helper template for detecting a safe conversion from another
      // unique_ptr
      template<typename _Up, typename _Ep>
        using __safe_conversion_up = __and_<
          is_convertible<typename unique_ptr<_Up, _Ep>::pointer, pointer>,
          __not_<is_array<_Up>>
        >;

    public:
      // Constructors.

      /// Default constructor, creates a unique_ptr that owns nothing.
      template<typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
        constexpr unique_ptr() noexcept
        : _M_t()
        { }

      /** Takes ownership of a pointer.
       *
       * @param __p  A pointer to an object of @c element_type
       *
       * The deleter will be value-initialized.
       */
      template<typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
        _GLIBCXX23_CONSTEXPR
        explicit
        unique_ptr(pointer __p) noexcept
        : _M_t(__p)
        { }

      /** Takes ownership of a pointer.
       *
       * @param __p  A pointer to an object of @c element_type
       * @param __d  A reference to a deleter.
       *
       * The deleter will be initialized with @p __d
       */
      template<typename _Del = deleter_type,
               typename = _Require<is_copy_constructible<_Del>>>
        _GLIBCXX23_CONSTEXPR
        unique_ptr(pointer __p, const deleter_type& __d) noexcept
        : _M_t(__p, __d) { }

      /** Takes ownership of a pointer.
       *
       * @param __p  A pointer to an object of @c element_type
       * @param __d  An rvalue reference to a (non-reference) deleter.
       *
       * The deleter will be initialized with @p std::move(__d)
       */
      template<typename _Del = deleter_type,
               typename = _Require<is_move_constructible<_Del>>>
        _GLIBCXX23_CONSTEXPR
        unique_ptr(pointer __p,
                   __enable_if_t<!is_lvalue_reference<_Del>::value,
                                 _Del&&> __d) noexcept
        : _M_t(__p, std::move(__d))
        { }

      template<typename _Del = deleter_type,
               typename _DelUnref = typename remove_reference<_Del>::type>
        _GLIBCXX23_CONSTEXPR
        unique_ptr(pointer,
                   __enable_if_t<is_lvalue_reference<_Del>::value,
                                 _DelUnref&&>) = delete;

      /// Creates a unique_ptr that owns nothing.
      template<typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
        constexpr unique_ptr(nullptr_t) noexcept
        : _M_t()
        { }

      // Move constructors.

      /// Move constructor.
      unique_ptr(unique_ptr&&) = default;

      /** @brief Converting constructor from another type
       *
       * Requires that the pointer owned by @p __u is convertible to the
       * type of pointer owned by this object, @p __u does not own an array,
       * and @p __u has a compatible deleter type.
       */
      template<typename _Up, typename _Ep, typename = _Require<
               __safe_conversion_up<_Up, _Ep>,
               __conditional_t<is_reference<_Dp>::value,
                               is_same<_Ep, _Dp>,
                               is_convertible<_Ep, _Dp>>>>
        _GLIBCXX23_CONSTEXPR
        unique_ptr(unique_ptr<_Up, _Ep>&& __u) noexcept
        : _M_t(__u.release(), std::forward<_Ep>(__u.get_deleter()))
        { }

#if _GLIBCXX_USE_DEPRECATED
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
      /// Converting constructor from @c auto_ptr
      template<typename _Up,
               typename = _Require<is_convertible<_Up*, pointer>,
                                   is_same<_Dp, default_delete<_Tp>>>>
        unique_ptr(auto_ptr<_Up>&& __u) noexcept;
#pragma GCC diagnostic pop
#endif

      /// Destructor, invokes the deleter if the stored pointer is not null.
#if __cplusplus > 202002L && __cpp_constexpr_dynamic_alloc
      constexpr
#endif
      ~unique_ptr() noexcept
      {
        static_assert(__is_invocable<deleter_type&, pointer>::value,
                      "unique_ptr's deleter must be invocable with a pointer");
        auto& __ptr = _M_t._M_ptr();
        if (__ptr != nullptr)
          get_deleter()(std::move(__ptr));
        __ptr = pointer();
      }

      // Assignment.

      /** @brief Move assignment operator.
       *
       * Invokes the deleter if this object owns a pointer.
       */
      unique_ptr& operator=(unique_ptr&&) = default;

      /** @brief Assignment from another type.
       *
       * @param __u  The object to transfer ownership from, which owns a
       *             convertible pointer to a non-array object.
       *
       * Invokes the deleter if this object owns a pointer.
       */
      template<typename _Up, typename _Ep>
        _GLIBCXX23_CONSTEXPR
        typename enable_if< __and_<
          __safe_conversion_up<_Up, _Ep>,
          is_assignable<deleter_type&, _Ep&&>
          >::value,
          unique_ptr&>::type
        operator=(unique_ptr<_Up, _Ep>&& __u) noexcept
        {
          reset(__u.release());
          get_deleter() = std::forward<_Ep>(__u.get_deleter());
          return *this;
        }

      /// Reset the %unique_ptr to empty, invoking the deleter if necessary.
      _GLIBCXX23_CONSTEXPR
      unique_ptr&
      operator=(nullptr_t) noexcept
      {
        reset();
        return *this;
      }

      // Observers.

      /// Dereference the stored pointer.
      _GLIBCXX23_CONSTEXPR
      typename add_lvalue_reference<element_type>::type
      operator*() const noexcept(noexcept(*std::declval<pointer>()))
      {
        __glibcxx_assert(get() != pointer());
        return *get();
      }

      /// Return the stored pointer.
      _GLIBCXX23_CONSTEXPR
      pointer
      operator->() const noexcept
      {
        _GLIBCXX_DEBUG_PEDASSERT(get() != pointer());
        return get();
      }

      /// Return the stored pointer.
      _GLIBCXX23_CONSTEXPR
      pointer
      get() const noexcept
      { return _M_t._M_ptr(); }

      /// Return a reference to the stored deleter.
      _GLIBCXX23_CONSTEXPR
      deleter_type&
      get_deleter() noexcept
      { return _M_t._M_deleter(); }

      /// Return a reference to the stored deleter.
      _GLIBCXX23_CONSTEXPR
      const deleter_type&
      get_deleter() const noexcept
      { return _M_t._M_deleter(); }

      /// Return @c true if the stored pointer is not null.
      _GLIBCXX23_CONSTEXPR
      explicit operator bool() const noexcept
      { return get() == pointer() ? false : true; }

      // Modifiers.

      /// Release ownership of any stored pointer.
      _GLIBCXX23_CONSTEXPR
      pointer
      release() noexcept
      { return _M_t.release(); }

      /** @brief Replace the stored pointer.
       *
       * @param __p  The new pointer to store.
       *
       * The deleter will be invoked if a pointer is already owned.
       */
      _GLIBCXX23_CONSTEXPR
      void
      reset(pointer __p = pointer()) noexcept
      {
        static_assert(__is_invocable<deleter_type&, pointer>::value,
                      "unique_ptr's deleter must be invocable with a pointer");
        _M_t.reset(std::move(__p));
      }

      /// Exchange the pointer and deleter with another object.
      _GLIBCXX23_CONSTEXPR
      void
      swap(unique_ptr& __u) noexcept
      {
        static_assert(__is_swappable<_Dp>::value, "deleter must be swappable");
        _M_t.swap(__u._M_t);
      }

      // Disable copy from lvalue.
      unique_ptr(const unique_ptr&) = delete;
      unique_ptr& operator=(const unique_ptr&) = delete;

    private:
#ifdef __glibcxx_out_ptr
      template<typename, typename, typename...>
        friend class out_ptr_t;
      template<typename, typename, typename...>
        friend class inout_ptr_t;
#endif
  };

  // 20.7.1.3 unique_ptr for array objects with a runtime length
  // [unique.ptr.runtime]
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // DR 740 - omit specialization for array objects with a compile time length

  /// A move-only smart pointer that manages unique ownership of an array.
  /// @headerfile memory
  /// @since C++11
  template<typename _Tp, typename _Dp>
    class unique_ptr<_Tp[], _Dp>
    {
      template <typename _Up>
      using _DeleterConstraint =
        typename __uniq_ptr_impl<_Tp, _Up>::_DeleterConstraint::type;

      __uniq_ptr_data<_Tp, _Dp> _M_t;

      // like is_base_of<_Tp, _Up> but false if unqualified types are the same
      template<typename _Up>
        using __is_derived_Tp
          = __and_< is_base_of<_Tp, _Up>,
                    __not_<is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up>>> >;

    public:
      using pointer       = typename __uniq_ptr_impl<_Tp, _Dp>::pointer;
      using element_type  = _Tp;
      using deleter_type  = _Dp;

      // helper template for detecting a safe conversion from another
      // unique_ptr
      template<typename _Up, typename _Ep,
               typename _UPtr = unique_ptr<_Up, _Ep>,
               typename _UP_pointer = typename _UPtr::pointer,
               typename _UP_element_type = typename _UPtr::element_type>
        using __safe_conversion_up = __and_<
          is_array<_Up>,
          is_same<pointer, element_type*>,
          is_same<_UP_pointer, _UP_element_type*>,
          is_convertible<_UP_element_type(*)[], element_type(*)[]>
        >;

      // helper template for detecting a safe conversion from a raw pointer
      template<typename _Up>
        using __safe_conversion_raw = __and_<
          __or_<__or_<is_same<_Up, pointer>,
                      is_same<_Up, nullptr_t>>,
                __and_<is_pointer<_Up>,
                       is_same<pointer, element_type*>,
                       is_convertible<
                         typename remove_pointer<_Up>::type(*)[],
                         element_type(*)[]>
                >
          >
        >;

      // Constructors.

      /// Default constructor, creates a unique_ptr that owns nothing.
      template<typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
        constexpr unique_ptr() noexcept
        : _M_t()
        { }

      /** Takes ownership of a pointer.
       *
       * @param __p  A pointer to an array of a type safely convertible
       * to an array of @c element_type
       *
       * The deleter will be value-initialized.
       */
      template<typename _Up,
               typename _Vp = _Dp,
               typename = _DeleterConstraint<_Vp>,
               typename = typename enable_if<
                 __safe_conversion_raw<_Up>::value, bool>::type>
        _GLIBCXX23_CONSTEXPR
        explicit
        unique_ptr(_Up __p) noexcept
        : _M_t(__p)
        { }

      /** Takes ownership of a pointer.
       *
       * @param __p  A pointer to an array of a type safely convertible
       * to an array of @c element_type
       * @param __d  A reference to a deleter.
       *
       * The deleter will be initialized with @p __d
       */
      template<typename _Up, typename _Del = deleter_type,
               typename = _Require<__safe_conversion_raw<_Up>,
                                   is_copy_constructible<_Del>>>
        _GLIBCXX23_CONSTEXPR
        unique_ptr(_Up __p, const deleter_type& __d) noexcept
        : _M_t(__p, __d) { }

      /** Takes ownership of a pointer.
       *
       * @param __p  A pointer to an array of a type safely convertible
       * to an array of @c element_type
       * @param __d  A reference to a deleter.
       *
       * The deleter will be initialized with @p std::move(__d)
       */
      template<typename _Up, typename _Del = deleter_type,
               typename = _Require<__safe_conversion_raw<_Up>,
                                   is_move_constructible<_Del>>>
        _GLIBCXX23_CONSTEXPR
        unique_ptr(_Up __p,
                   __enable_if_t<!is_lvalue_reference<_Del>::value,
                                 _Del&&> __d) noexcept
        : _M_t(std::move(__p), std::move(__d))
        { }

      template<typename _Up, typename _Del = deleter_type,
               typename _DelUnref = typename remove_reference<_Del>::type,
               typename = _Require<__safe_conversion_raw<_Up>>>
        unique_ptr(_Up,
                   __enable_if_t<is_lvalue_reference<_Del>::value,
                                 _DelUnref&&>) = delete;

      /// Move constructor.
      unique_ptr(unique_ptr&&) = default;

      /// Creates a unique_ptr that owns nothing.
      template<typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
        constexpr unique_ptr(nullptr_t) noexcept
        : _M_t()
        { }

      template<typename _Up, typename _Ep, typename = _Require<
               __safe_conversion_up<_Up, _Ep>,
               __conditional_t<is_reference<_Dp>::value,
                               is_same<_Ep, _Dp>,
                               is_convertible<_Ep, _Dp>>>>
        _GLIBCXX23_CONSTEXPR
        unique_ptr(unique_ptr<_Up, _Ep>&& __u) noexcept
        : _M_t(__u.release(), std::forward<_Ep>(__u.get_deleter()))
        { }

      /// Destructor, invokes the deleter if the stored pointer is not null.
#if __cplusplus > 202002L && __cpp_constexpr_dynamic_alloc
      constexpr
#endif
      ~unique_ptr()
      {
        auto& __ptr = _M_t._M_ptr();
        if (__ptr != nullptr)
          get_deleter()(__ptr);
        __ptr = pointer();
      }

      // Assignment.

      /** @brief Move assignment operator.
       *
       * Invokes the deleter if this object owns a pointer.
       */
      unique_ptr&
      operator=(unique_ptr&&) = default;

      /** @brief Assignment from another type.
       *
       * @param __u  The object to transfer ownership from, which owns a
       *             convertible pointer to an array object.
       *
       * Invokes the deleter if this object owns a pointer.
       */
      template<typename _Up, typename _Ep>
        _GLIBCXX23_CONSTEXPR
        typename
        enable_if<__and_<__safe_conversion_up<_Up, _Ep>,
                         is_assignable<deleter_type&, _Ep&&>
                  >::value,
                  unique_ptr&>::type
        operator=(unique_ptr<_Up, _Ep>&& __u) noexcept
        {
          reset(__u.release());
          get_deleter() = std::forward<_Ep>(__u.get_deleter());
          return *this;
        }

      /// Reset the %unique_ptr to empty, invoking the deleter if necessary.
      _GLIBCXX23_CONSTEXPR
      unique_ptr&
      operator=(nullptr_t) noexcept
      {
        reset();
        return *this;
      }

      // Observers.

      /// Access an element of owned array.
      _GLIBCXX23_CONSTEXPR
      typename std::add_lvalue_reference<element_type>::type
      operator[](size_t __i) const
      {
        __glibcxx_assert(get() != pointer());
        return get()[__i];
      }

      /// Return the stored pointer.
      _GLIBCXX23_CONSTEXPR
      pointer
      get() const noexcept
      { return _M_t._M_ptr(); }

      /// Return a reference to the stored deleter.
      _GLIBCXX23_CONSTEXPR
      deleter_type&
      get_deleter() noexcept
      { return _M_t._M_deleter(); }

      /// Return a reference to the stored deleter.
      _GLIBCXX23_CONSTEXPR
      const deleter_type&
      get_deleter() const noexcept
      { return _M_t._M_deleter(); }

      /// Return @c true if the stored pointer is not null.
      _GLIBCXX23_CONSTEXPR
      explicit operator bool() const noexcept
      { return get() == pointer() ? false : true; }

      // Modifiers.

      /// Release ownership of any stored pointer.
      _GLIBCXX23_CONSTEXPR
      pointer
      release() noexcept
      { return _M_t.release(); }

      /** @brief Replace the stored pointer.
       *
       * @param __p  The new pointer to store.
       *
       * The deleter will be invoked if a pointer is already owned.
       */
      template <typename _Up,
                typename = _Require<
                  __or_<is_same<_Up, pointer>,
                        __and_<is_same<pointer, element_type*>,
                               is_pointer<_Up>,
                               is_convertible<
                                 typename remove_pointer<_Up>::type(*)[],
                                 element_type(*)[]
                               >
                        >
                  >
               >>
      _GLIBCXX23_CONSTEXPR
      void
      reset(_Up __p) noexcept
      { _M_t.reset(std::move(__p)); }

      _GLIBCXX23_CONSTEXPR
      void reset(nullptr_t = nullptr) noexcept
      { reset(pointer()); }

      /// Exchange the pointer and deleter with another object.
      _GLIBCXX23_CONSTEXPR
      void
      swap(unique_ptr& __u) noexcept
      {
        static_assert(__is_swappable<_Dp>::value, "deleter must be swappable");
        _M_t.swap(__u._M_t);
      }

      // Disable copy from lvalue.
      unique_ptr(const unique_ptr&) = delete;
      unique_ptr& operator=(const unique_ptr&) = delete;

    private:
#ifdef __glibcxx_out_ptr
      template<typename, typename, typename...> friend class out_ptr_t;
      template<typename, typename, typename...> friend class inout_ptr_t;
#endif
    };

  /// @{
  /// @relates unique_ptr

  /// Swap overload for unique_ptr
  template<typename _Tp, typename _Dp>
    inline
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
    // Constrained free swap overload, see p0185r1
    _GLIBCXX23_CONSTEXPR
    typename enable_if<__is_swappable<_Dp>::value>::type
#else
    void
#endif
    swap(unique_ptr<_Tp, _Dp>& __x,
         unique_ptr<_Tp, _Dp>& __y) noexcept
    { __x.swap(__y); }

#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
  template<typename _Tp, typename _Dp>
    typename enable_if<!__is_swappable<_Dp>::value>::type
    swap(unique_ptr<_Tp, _Dp>&,
         unique_ptr<_Tp, _Dp>&) = delete;
#endif

  /// Equality operator for unique_ptr objects, compares the owned pointers
  template<typename _Tp, typename _Dp,
           typename _Up, typename _Ep>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator==(const unique_ptr<_Tp, _Dp>& __x,
               const unique_ptr<_Up, _Ep>& __y)
    { return __x.get() == __y.get(); }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator==(const unique_ptr<_Tp, _Dp>& __x, nullptr_t) noexcept
    { return !__x; }

#ifndef __cpp_lib_three_way_comparison
  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD
    inline bool
    operator==(nullptr_t, const unique_ptr<_Tp, _Dp>& __x) noexcept
    { return !__x; }

  /// Inequality operator for unique_ptr objects, compares the owned pointers
  template<typename _Tp, typename _Dp,
           typename _Up, typename _Ep>
    _GLIBCXX_NODISCARD
    inline bool
    operator!=(const unique_ptr<_Tp, _Dp>& __x,
               const unique_ptr<_Up, _Ep>& __y)
    { return __x.get() != __y.get(); }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD
    inline bool
    operator!=(const unique_ptr<_Tp, _Dp>& __x, nullptr_t) noexcept
    { return (bool)__x; }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD
    inline bool
    operator!=(nullptr_t, const unique_ptr<_Tp, _Dp>& __x) noexcept
    { return (bool)__x; }
#endif // three way comparison

  /// Relational operator for unique_ptr objects, compares the owned pointers
  template<typename _Tp, typename _Dp,
           typename _Up, typename _Ep>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator<(const unique_ptr<_Tp, _Dp>& __x,
              const unique_ptr<_Up, _Ep>& __y)
    {
      typedef typename
        std::common_type<typename unique_ptr<_Tp, _Dp>::pointer,
                         typename unique_ptr<_Up, _Ep>::pointer>::type _CT;
      return std::less<_CT>()(__x.get(), __y.get());
    }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator<(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
    {
      return std::less<typename unique_ptr<_Tp, _Dp>::pointer>()(__x.get(),
                                                                 nullptr);
    }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator<(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
    {
      return std::less<typename unique_ptr<_Tp, _Dp>::pointer>()(nullptr,
                                                                 __x.get());
    }

  /// Relational operator for unique_ptr objects, compares the owned pointers
  template<typename _Tp, typename _Dp,
           typename _Up, typename _Ep>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator<=(const unique_ptr<_Tp, _Dp>& __x,
               const unique_ptr<_Up, _Ep>& __y)
    { return !(__y < __x); }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator<=(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
    { return !(nullptr < __x); }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator<=(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
    { return !(__x < nullptr); }

  /// Relational operator for unique_ptr objects, compares the owned pointers
  template<typename _Tp, typename _Dp,
           typename _Up, typename _Ep>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator>(const unique_ptr<_Tp, _Dp>& __x,
              const unique_ptr<_Up, _Ep>& __y)
    { return (__y < __x); }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator>(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
    {
      return std::less<typename unique_ptr<_Tp, _Dp>::pointer>()(nullptr,
                                                                 __x.get());
    }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator>(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
    {
      return std::less<typename unique_ptr<_Tp, _Dp>::pointer>()(__x.get(),
                                                                 nullptr);
    }

  /// Relational operator for unique_ptr objects, compares the owned pointers
  template<typename _Tp, typename _Dp,
           typename _Up, typename _Ep>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator>=(const unique_ptr<_Tp, _Dp>& __x,
               const unique_ptr<_Up, _Ep>& __y)
    { return !(__x < __y); }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD _GLIBCXX23_CONSTEXPR
    inline bool
    operator>=(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
    { return !(__x < nullptr); }

  /// unique_ptr comparison with nullptr
  template<typename _Tp, typename _Dp>
    _GLIBCXX_NODISCARD inline bool
    operator>=(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
    { return !(nullptr < __x); }

#ifdef __cpp_lib_three_way_comparison
  template<typename _Tp, typename _Dp, typename _Up, typename _Ep>
    requires three_way_comparable_with<typename unique_ptr<_Tp, _Dp>::pointer,
                                       typename unique_ptr<_Up, _Ep>::pointer>
    _GLIBCXX23_CONSTEXPR
    inline
    compare_three_way_result_t<typename unique_ptr<_Tp, _Dp>::pointer,
                               typename unique_ptr<_Up, _Ep>::pointer>
    operator<=>(const unique_ptr<_Tp, _Dp>& __x,
                const unique_ptr<_Up, _Ep>& __y)
    { return compare_three_way()(__x.get(), __y.get()); }

  template<typename _Tp, typename _Dp>
    requires three_way_comparable<typename unique_ptr<_Tp, _Dp>::pointer>
    _GLIBCXX23_CONSTEXPR
    inline
    compare_three_way_result_t<typename unique_ptr<_Tp, _Dp>::pointer>
    operator<=>(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
    {
      using pointer = typename unique_ptr<_Tp, _Dp>::pointer;
      return compare_three_way()(__x.get(), static_cast<pointer>(nullptr));
    }
#endif
  /// @} relates unique_ptr

  /// @cond undocumented
  template<typename _Up, typename _Ptr = typename _Up::pointer,
           bool = __poison_hash<_Ptr>::__enable_hash_call>
    struct __uniq_ptr_hash
#if ! _GLIBCXX_INLINE_VERSION
    : private __poison_hash<_Ptr>
#endif
    {
      size_t
      operator()(const _Up& __u) const
      noexcept(noexcept(std::declval<hash<_Ptr>>()(std::declval<_Ptr>())))
      { return hash<_Ptr>()(__u.get()); }
    };

  template<typename _Up, typename _Ptr>
    struct __uniq_ptr_hash<_Up, _Ptr, false>
    : private __poison_hash<_Ptr>
    { };
  /// @endcond

  /// std::hash specialization for unique_ptr.
  template<typename _Tp, typename _Dp>
    struct hash<unique_ptr<_Tp, _Dp>>
    : public __hash_base<size_t, unique_ptr<_Tp, _Dp>>,
      public __uniq_ptr_hash<unique_ptr<_Tp, _Dp>>
    { };

#ifdef __glibcxx_make_unique // C++ >= 14 && HOSTED
  /// @cond undocumented
namespace __detail
{
  template<typename _Tp>
    struct _MakeUniq
    { typedef unique_ptr<_Tp> __single_object; };

  template<typename _Tp>
    struct _MakeUniq<_Tp[]>
    { typedef unique_ptr<_Tp[]> __array; };

  template<typename _Tp, size_t _Bound>
    struct _MakeUniq<_Tp[_Bound]>
    { struct __invalid_type { }; };

  template<typename _Tp>
    using __unique_ptr_t = typename _MakeUniq<_Tp>::__single_object;
  template<typename _Tp>
    using __unique_ptr_array_t = typename _MakeUniq<_Tp>::__array;
  template<typename _Tp>
    using __invalid_make_unique_t = typename _MakeUniq<_Tp>::__invalid_type;
}
  /// @endcond

  /** Create an object owned by a `unique_ptr`.
   *  @tparam _Tp A non-array object type.
   *  @param __args Constructor arguments for the new object.
   *  @returns A `unique_ptr<_Tp>` that owns the new object.
   *  @since C++14
   *  @relates unique_ptr
   */
  template<typename _Tp, typename... _Args>
    _GLIBCXX23_CONSTEXPR
    inline __detail::__unique_ptr_t<_Tp>
    make_unique(_Args&&... __args)
    { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }

  /** Create an array owned by a `unique_ptr`.
   *  @tparam _Tp An array type of unknown bound, such as `U[]`.
   *  @param __num The number of elements of type `U` in the new array.
   *  @returns A `unique_ptr<U[]>` that owns the new array.
   *  @since C++14
   *  @relates unique_ptr
   *
   *  The array elements are value-initialized.
   */
  template<typename _Tp>
    _GLIBCXX23_CONSTEXPR
    inline __detail::__unique_ptr_array_t<_Tp>
    make_unique(size_t __num)
    { return unique_ptr<_Tp>(new remove_extent_t<_Tp>[__num]()); }

  /** Disable std::make_unique for arrays of known bound.
   *  @tparam _Tp An array type of known bound, such as `U[N]`.
   *  @since C++14
   *  @relates unique_ptr
   */
  template<typename _Tp, typename... _Args>
    __detail::__invalid_make_unique_t<_Tp>
    make_unique(_Args&&...) = delete;

#if __cplusplus > 201703L
  /** Create a default-initialied object owned by a `unique_ptr`.
   *  @tparam _Tp A non-array object type.
   *  @returns A `unique_ptr<_Tp>` that owns the new object.
   *  @since C++20
   *  @relates unique_ptr
   */
  template<typename _Tp>
    _GLIBCXX23_CONSTEXPR
    inline __detail::__unique_ptr_t<_Tp>
    make_unique_for_overwrite()
    { return unique_ptr<_Tp>(new _Tp); }

  /** Create a default-initialized array owned by a `unique_ptr`.
   *  @tparam _Tp An array type of unknown bound, such as `U[]`.
   *  @param __num The number of elements of type `U` in the new array.
   *  @returns A `unique_ptr<U[]>` that owns the new array.
   *  @since C++20
   *  @relates unique_ptr
   */
  template<typename _Tp>
    _GLIBCXX23_CONSTEXPR
    inline __detail::__unique_ptr_array_t<_Tp>
    make_unique_for_overwrite(size_t __num)
    { return unique_ptr<_Tp>(new remove_extent_t<_Tp>[__num]); }

  /** Disable std::make_unique_for_overwrite for arrays of known bound.
   *  @tparam _Tp An array type of known bound, such as `U[N]`.
   *  @since C++20
   *  @relates unique_ptr
   */
  template<typename _Tp, typename... _Args>
    __detail::__invalid_make_unique_t<_Tp>
    make_unique_for_overwrite(_Args&&...) = delete;
#endif // C++20

#endif // C++14 && HOSTED

#if __cplusplus > 201703L && __cpp_concepts && _GLIBCXX_HOSTED
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2948. unique_ptr does not define operator<< for stream output
  /// Stream output operator for unique_ptr
  /// @relates unique_ptr
  /// @since C++20
  template<typename _CharT, typename _Traits, typename _Tp, typename _Dp>
    inline basic_ostream<_CharT, _Traits>&
    operator<<(basic_ostream<_CharT, _Traits>& __os,
               const unique_ptr<_Tp, _Dp>& __p)
    requires requires { __os << __p.get(); }
    {
      __os << __p.get();
      return __os;
    }
#endif // C++20 && HOSTED

#if __cpp_variable_templates
  template<typename _Tp>
    static constexpr bool __is_unique_ptr = false;
  template<typename _Tp, typename _Del>
    static constexpr bool __is_unique_ptr<unique_ptr<_Tp, _Del>> = true;
#endif

  /// @} group pointer_abstractions

#if __cplusplus >= 201703L
  namespace __detail::__variant
  {
    template<typename> struct _Never_valueless_alt; // see <variant>

    // Provide the strong exception-safety guarantee when emplacing a
    // unique_ptr into a variant.
    template<typename _Tp, typename _Del>
      struct _Never_valueless_alt<std::unique_ptr<_Tp, _Del>>
      : std::true_type
      { };
  }  // namespace __detail::__variant
#endif // C++17

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* _UNIQUE_PTR_H */