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gcc/libstdc++-v3/include/bits/shared_ptr.h
Jakub Jelinek 99dee82307 Update copyright years.
2021-01-04 10:26:59 +01:00

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// shared_ptr and weak_ptr implementation -*- 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/>.
// GCC Note: Based on files from version 1.32.0 of the Boost library.
// shared_count.hpp
// Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
// shared_ptr.hpp
// Copyright (C) 1998, 1999 Greg Colvin and Beman Dawes.
// Copyright (C) 2001, 2002, 2003 Peter Dimov
// weak_ptr.hpp
// Copyright (C) 2001, 2002, 2003 Peter Dimov
// enable_shared_from_this.hpp
// Copyright (C) 2002 Peter Dimov
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
/** @file
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{memory}
*/
#ifndef _SHARED_PTR_H
#define _SHARED_PTR_H 1
#include <iosfwd> // std::basic_ostream
#include <bits/shared_ptr_base.h>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @addtogroup pointer_abstractions
* @{
*/
// 20.7.2.2.11 shared_ptr I/O
/// Write the stored pointer to an ostream.
/// @relates shared_ptr
template<typename _Ch, typename _Tr, typename _Tp, _Lock_policy _Lp>
inline std::basic_ostream<_Ch, _Tr>&
operator<<(std::basic_ostream<_Ch, _Tr>& __os,
const __shared_ptr<_Tp, _Lp>& __p)
{
__os << __p.get();
return __os;
}
template<typename _Del, typename _Tp, _Lock_policy _Lp>
inline _Del*
get_deleter(const __shared_ptr<_Tp, _Lp>& __p) noexcept
{
#if __cpp_rtti
return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
#else
return 0;
#endif
}
/// 20.7.2.2.10 shared_ptr get_deleter
/// If `__p` has a deleter of type `_Del`, return a pointer to it.
/// @relates shared_ptr
template<typename _Del, typename _Tp>
inline _Del*
get_deleter(const shared_ptr<_Tp>& __p) noexcept
{
#if __cpp_rtti
return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
#else
return 0;
#endif
}
/**
* @brief A smart pointer with reference-counted copy semantics.
*
* A `shared_ptr` object is either empty or _owns_ a pointer passed
* to the constructor. Copies of a `shared_ptr` share ownership of
* the same pointer. When the last `shared_ptr` that owns the pointer
* is destroyed or reset, the owned pointer is freed (either by `delete`
* or by invoking a custom deleter that was passed to the constructor).
*
* A `shared_ptr` also stores another pointer, which is usually
* (but not always) the same pointer as it owns. The stored pointer
* can be retrieved by calling the `get()` member function.
*
* The equality and relational operators for `shared_ptr` only compare
* the stored pointer returned by `get()`, not the owned pointer.
* To test whether two `shared_ptr` objects share ownership of the same
* pointer see `std::shared_ptr::owner_before` and `std::owner_less`.
*/
template<typename _Tp>
class shared_ptr : public __shared_ptr<_Tp>
{
template<typename... _Args>
using _Constructible = typename enable_if<
is_constructible<__shared_ptr<_Tp>, _Args...>::value
>::type;
template<typename _Arg>
using _Assignable = typename enable_if<
is_assignable<__shared_ptr<_Tp>&, _Arg>::value, shared_ptr&
>::type;
public:
/// The type pointed to by the stored pointer, remove_extent_t<_Tp>
using element_type = typename __shared_ptr<_Tp>::element_type;
#if __cplusplus >= 201703L
# define __cpp_lib_shared_ptr_weak_type 201606
/// The corresponding weak_ptr type for this shared_ptr
using weak_type = weak_ptr<_Tp>;
#endif
/**
* @brief Construct an empty %shared_ptr.
* @post use_count()==0 && get()==0
*/
constexpr shared_ptr() noexcept : __shared_ptr<_Tp>() { }
shared_ptr(const shared_ptr&) noexcept = default; ///< Copy constructor
/**
* @brief Construct a %shared_ptr that owns the pointer @a __p.
* @param __p A pointer that is convertible to element_type*.
* @post use_count() == 1 && get() == __p
* @throw std::bad_alloc, in which case @c delete @a __p is called.
*/
template<typename _Yp, typename = _Constructible<_Yp*>>
explicit
shared_ptr(_Yp* __p) : __shared_ptr<_Tp>(__p) { }
/**
* @brief Construct a %shared_ptr that owns the pointer @a __p
* and the deleter @a __d.
* @param __p A pointer.
* @param __d A deleter.
* @post use_count() == 1 && get() == __p
* @throw std::bad_alloc, in which case @a __d(__p) is called.
*
* Requirements: _Deleter's copy constructor and destructor must
* not throw
*
* __shared_ptr will release __p by calling __d(__p)
*/
template<typename _Yp, typename _Deleter,
typename = _Constructible<_Yp*, _Deleter>>
shared_ptr(_Yp* __p, _Deleter __d)
: __shared_ptr<_Tp>(__p, std::move(__d)) { }
/**
* @brief Construct a %shared_ptr that owns a null pointer
* and the deleter @a __d.
* @param __p A null pointer constant.
* @param __d A deleter.
* @post use_count() == 1 && get() == __p
* @throw std::bad_alloc, in which case @a __d(__p) is called.
*
* Requirements: _Deleter's copy constructor and destructor must
* not throw
*
* The last owner will call __d(__p)
*/
template<typename _Deleter>
shared_ptr(nullptr_t __p, _Deleter __d)
: __shared_ptr<_Tp>(__p, std::move(__d)) { }
/**
* @brief Construct a %shared_ptr that owns the pointer @a __p
* and the deleter @a __d.
* @param __p A pointer.
* @param __d A deleter.
* @param __a An allocator.
* @post use_count() == 1 && get() == __p
* @throw std::bad_alloc, in which case @a __d(__p) is called.
*
* Requirements: _Deleter's copy constructor and destructor must
* not throw _Alloc's copy constructor and destructor must not
* throw.
*
* __shared_ptr will release __p by calling __d(__p)
*/
template<typename _Yp, typename _Deleter, typename _Alloc,
typename = _Constructible<_Yp*, _Deleter, _Alloc>>
shared_ptr(_Yp* __p, _Deleter __d, _Alloc __a)
: __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
/**
* @brief Construct a %shared_ptr that owns a null pointer
* and the deleter @a __d.
* @param __p A null pointer constant.
* @param __d A deleter.
* @param __a An allocator.
* @post use_count() == 1 && get() == __p
* @throw std::bad_alloc, in which case @a __d(__p) is called.
*
* Requirements: _Deleter's copy constructor and destructor must
* not throw _Alloc's copy constructor and destructor must not
* throw.
*
* The last owner will call __d(__p)
*/
template<typename _Deleter, typename _Alloc>
shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
: __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
// Aliasing constructor
/**
* @brief Constructs a `shared_ptr` instance that stores `__p`
* and shares ownership with `__r`.
* @param __r A `shared_ptr`.
* @param __p A pointer that will remain valid while `*__r` is valid.
* @post `get() == __p && use_count() == __r.use_count()`
*
* This can be used to construct a `shared_ptr` to a sub-object
* of an object managed by an existing `shared_ptr`. The complete
* object will remain valid while any `shared_ptr` owns it, even
* if they don't store a pointer to the complete object.
*
* @code
* shared_ptr<pair<int,int>> pii(new pair<int,int>());
* shared_ptr<int> pi(pii, &pii->first);
* assert(pii.use_count() == 2);
* @endcode
*/
template<typename _Yp>
shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) noexcept
: __shared_ptr<_Tp>(__r, __p) { }
#if __cplusplus > 201703L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2996. Missing rvalue overloads for shared_ptr operations
/**
* @brief Constructs a `shared_ptr` instance that stores `__p`
* and shares ownership with `__r`.
* @param __r A `shared_ptr`.
* @param __p A pointer that will remain valid while `*__r` is valid.
* @post `get() == __p && !__r.use_count() && !__r.get()`
*
* This can be used to construct a `shared_ptr` to a sub-object
* of an object managed by an existing `shared_ptr`. The complete
* object will remain valid while any `shared_ptr` owns it, even
* if they don't store a pointer to the complete object.
*
* @code
* shared_ptr<pair<int,int>> pii(new pair<int,int>());
* shared_ptr<int> pi1(pii, &pii->first);
* assert(pii.use_count() == 2);
* shared_ptr<int> pi2(std::move(pii), &pii->second);
* assert(pii.use_count() == 0);
* @endcode
*/
template<typename _Yp>
shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
: __shared_ptr<_Tp>(std::move(__r), __p) { }
#endif
/**
* @brief If @a __r is empty, constructs an empty %shared_ptr;
* otherwise construct a %shared_ptr that shares ownership
* with @a __r.
* @param __r A %shared_ptr.
* @post get() == __r.get() && use_count() == __r.use_count()
*/
template<typename _Yp,
typename = _Constructible<const shared_ptr<_Yp>&>>
shared_ptr(const shared_ptr<_Yp>& __r) noexcept
: __shared_ptr<_Tp>(__r) { }
/**
* @brief Move-constructs a %shared_ptr instance from @a __r.
* @param __r A %shared_ptr rvalue.
* @post *this contains the old value of @a __r, @a __r is empty.
*/
shared_ptr(shared_ptr&& __r) noexcept
: __shared_ptr<_Tp>(std::move(__r)) { }
/**
* @brief Move-constructs a %shared_ptr instance from @a __r.
* @param __r A %shared_ptr rvalue.
* @post *this contains the old value of @a __r, @a __r is empty.
*/
template<typename _Yp, typename = _Constructible<shared_ptr<_Yp>>>
shared_ptr(shared_ptr<_Yp>&& __r) noexcept
: __shared_ptr<_Tp>(std::move(__r)) { }
/**
* @brief Constructs a %shared_ptr that shares ownership with @a __r
* and stores a copy of the pointer stored in @a __r.
* @param __r A weak_ptr.
* @post use_count() == __r.use_count()
* @throw bad_weak_ptr when __r.expired(),
* in which case the constructor has no effect.
*/
template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
explicit shared_ptr(const weak_ptr<_Yp>& __r)
: __shared_ptr<_Tp>(__r) { }
#if _GLIBCXX_USE_DEPRECATED
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
template<typename _Yp, typename = _Constructible<auto_ptr<_Yp>>>
shared_ptr(auto_ptr<_Yp>&& __r);
#pragma GCC diagnostic pop
#endif
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2399. shared_ptr's constructor from unique_ptr should be constrained
template<typename _Yp, typename _Del,
typename = _Constructible<unique_ptr<_Yp, _Del>>>
shared_ptr(unique_ptr<_Yp, _Del>&& __r)
: __shared_ptr<_Tp>(std::move(__r)) { }
#if __cplusplus <= 201402L && _GLIBCXX_USE_DEPRECATED
// This non-standard constructor exists to support conversions that
// were possible in C++11 and C++14 but are ill-formed in C++17.
// If an exception is thrown this constructor has no effect.
template<typename _Yp, typename _Del,
_Constructible<unique_ptr<_Yp, _Del>, __sp_array_delete>* = 0>
shared_ptr(unique_ptr<_Yp, _Del>&& __r)
: __shared_ptr<_Tp>(std::move(__r), __sp_array_delete()) { }
#endif
/**
* @brief Construct an empty %shared_ptr.
* @post use_count() == 0 && get() == nullptr
*/
constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
shared_ptr& operator=(const shared_ptr&) noexcept = default;
template<typename _Yp>
_Assignable<const shared_ptr<_Yp>&>
operator=(const shared_ptr<_Yp>& __r) noexcept
{
this->__shared_ptr<_Tp>::operator=(__r);
return *this;
}
#if _GLIBCXX_USE_DEPRECATED
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
template<typename _Yp>
_Assignable<auto_ptr<_Yp>>
operator=(auto_ptr<_Yp>&& __r)
{
this->__shared_ptr<_Tp>::operator=(std::move(__r));
return *this;
}
#pragma GCC diagnostic pop
#endif
shared_ptr&
operator=(shared_ptr&& __r) noexcept
{
this->__shared_ptr<_Tp>::operator=(std::move(__r));
return *this;
}
template<class _Yp>
_Assignable<shared_ptr<_Yp>>
operator=(shared_ptr<_Yp>&& __r) noexcept
{
this->__shared_ptr<_Tp>::operator=(std::move(__r));
return *this;
}
template<typename _Yp, typename _Del>
_Assignable<unique_ptr<_Yp, _Del>>
operator=(unique_ptr<_Yp, _Del>&& __r)
{
this->__shared_ptr<_Tp>::operator=(std::move(__r));
return *this;
}
private:
// This constructor is non-standard, it is used by allocate_shared.
template<typename _Alloc, typename... _Args>
shared_ptr(_Sp_alloc_shared_tag<_Alloc> __tag, _Args&&... __args)
: __shared_ptr<_Tp>(__tag, std::forward<_Args>(__args)...)
{ }
template<typename _Yp, typename _Alloc, typename... _Args>
friend shared_ptr<_Yp>
allocate_shared(const _Alloc& __a, _Args&&... __args);
// This constructor is non-standard, it is used by weak_ptr::lock().
shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t) noexcept
: __shared_ptr<_Tp>(__r, std::nothrow) { }
friend class weak_ptr<_Tp>;
};
#if __cpp_deduction_guides >= 201606
template<typename _Tp>
shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
template<typename _Tp, typename _Del>
shared_ptr(unique_ptr<_Tp, _Del>) -> shared_ptr<_Tp>;
#endif
// 20.7.2.2.7 shared_ptr comparisons
/// @relates shared_ptr @{
/// Equality operator for shared_ptr objects, compares the stored pointers
template<typename _Tp, typename _Up>
_GLIBCXX_NODISCARD inline bool
operator==(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
{ return __a.get() == __b.get(); }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
{ return !__a; }
#ifdef __cpp_lib_three_way_comparison
template<typename _Tp, typename _Up>
inline strong_ordering
operator<=>(const shared_ptr<_Tp>& __a,
const shared_ptr<_Up>& __b) noexcept
{ return compare_three_way()(__a.get(), __b.get()); }
template<typename _Tp>
inline strong_ordering
operator<=>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
{
using pointer = typename shared_ptr<_Tp>::element_type*;
return compare_three_way()(__a.get(), static_cast<pointer>(nullptr));
}
#else
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
{ return !__a; }
/// Inequality operator for shared_ptr objects, compares the stored pointers
template<typename _Tp, typename _Up>
_GLIBCXX_NODISCARD inline bool
operator!=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
{ return __a.get() != __b.get(); }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
{ return (bool)__a; }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
{ return (bool)__a; }
/// Relational operator for shared_ptr objects, compares the stored pointers
template<typename _Tp, typename _Up>
_GLIBCXX_NODISCARD inline bool
operator<(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
{
using _Tp_elt = typename shared_ptr<_Tp>::element_type;
using _Up_elt = typename shared_ptr<_Up>::element_type;
using _Vp = typename common_type<_Tp_elt*, _Up_elt*>::type;
return less<_Vp>()(__a.get(), __b.get());
}
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
{
using _Tp_elt = typename shared_ptr<_Tp>::element_type;
return less<_Tp_elt*>()(__a.get(), nullptr);
}
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
{
using _Tp_elt = typename shared_ptr<_Tp>::element_type;
return less<_Tp_elt*>()(nullptr, __a.get());
}
/// Relational operator for shared_ptr objects, compares the stored pointers
template<typename _Tp, typename _Up>
_GLIBCXX_NODISCARD inline bool
operator<=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
{ return !(__b < __a); }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
{ return !(nullptr < __a); }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
{ return !(__a < nullptr); }
/// Relational operator for shared_ptr objects, compares the stored pointers
template<typename _Tp, typename _Up>
_GLIBCXX_NODISCARD inline bool
operator>(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
{ return (__b < __a); }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
{ return nullptr < __a; }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
{ return __a < nullptr; }
/// Relational operator for shared_ptr objects, compares the stored pointers
template<typename _Tp, typename _Up>
_GLIBCXX_NODISCARD inline bool
operator>=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
{ return !(__a < __b); }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
{ return !(__a < nullptr); }
/// shared_ptr comparison with nullptr
template<typename _Tp>
_GLIBCXX_NODISCARD inline bool
operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
{ return !(nullptr < __a); }
#endif
// 20.7.2.2.8 shared_ptr specialized algorithms.
/// Swap overload for shared_ptr
template<typename _Tp>
inline void
swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
{ __a.swap(__b); }
// 20.7.2.2.9 shared_ptr casts.
/// Convert type of `shared_ptr`, via `static_cast`
template<typename _Tp, typename _Up>
inline shared_ptr<_Tp>
static_pointer_cast(const shared_ptr<_Up>& __r) noexcept
{
using _Sp = shared_ptr<_Tp>;
return _Sp(__r, static_cast<typename _Sp::element_type*>(__r.get()));
}
/// Convert type of `shared_ptr`, via `const_cast`
template<typename _Tp, typename _Up>
inline shared_ptr<_Tp>
const_pointer_cast(const shared_ptr<_Up>& __r) noexcept
{
using _Sp = shared_ptr<_Tp>;
return _Sp(__r, const_cast<typename _Sp::element_type*>(__r.get()));
}
/// Convert type of `shared_ptr`, via `dynamic_cast`
template<typename _Tp, typename _Up>
inline shared_ptr<_Tp>
dynamic_pointer_cast(const shared_ptr<_Up>& __r) noexcept
{
using _Sp = shared_ptr<_Tp>;
if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
return _Sp(__r, __p);
return _Sp();
}
#if __cplusplus >= 201703L
/// Convert type of `shared_ptr`, via `reinterpret_cast`
template<typename _Tp, typename _Up>
inline shared_ptr<_Tp>
reinterpret_pointer_cast(const shared_ptr<_Up>& __r) noexcept
{
using _Sp = shared_ptr<_Tp>;
return _Sp(__r, reinterpret_cast<typename _Sp::element_type*>(__r.get()));
}
#if __cplusplus > 201703L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2996. Missing rvalue overloads for shared_ptr operations
/// Convert type of `shared_ptr` rvalue, via `static_cast`
template<typename _Tp, typename _Up>
inline shared_ptr<_Tp>
static_pointer_cast(shared_ptr<_Up>&& __r) noexcept
{
using _Sp = shared_ptr<_Tp>;
return _Sp(std::move(__r),
static_cast<typename _Sp::element_type*>(__r.get()));
}
/// Convert type of `shared_ptr` rvalue, via `const_cast`
template<typename _Tp, typename _Up>
inline shared_ptr<_Tp>
const_pointer_cast(shared_ptr<_Up>&& __r) noexcept
{
using _Sp = shared_ptr<_Tp>;
return _Sp(std::move(__r),
const_cast<typename _Sp::element_type*>(__r.get()));
}
/// Convert type of `shared_ptr` rvalue, via `dynamic_cast`
template<typename _Tp, typename _Up>
inline shared_ptr<_Tp>
dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept
{
using _Sp = shared_ptr<_Tp>;
if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
return _Sp(std::move(__r), __p);
return _Sp();
}
/// Convert type of `shared_ptr` rvalue, via `reinterpret_cast`
template<typename _Tp, typename _Up>
inline shared_ptr<_Tp>
reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept
{
using _Sp = shared_ptr<_Tp>;
return _Sp(std::move(__r),
reinterpret_cast<typename _Sp::element_type*>(__r.get()));
}
#endif // C++20
#endif // C++17
// @}
/**
* @brief A non-owning observer for a pointer owned by a shared_ptr
*
* A weak_ptr provides a safe alternative to a raw pointer when you want
* a non-owning reference to an object that is managed by a shared_ptr.
*
* Unlike a raw pointer, a weak_ptr can be converted to a new shared_ptr
* that shares ownership with every other shared_ptr that already owns
* the pointer. In other words you can upgrade from a non-owning "weak"
* reference to an owning shared_ptr, without having access to any of
* the existing shared_ptr objects.
*
* Also unlike a raw pointer, a weak_ptr does not become "dangling" after
* the object it points to has been destroyed. Instead, a weak_ptr
* becomes _expired_ and can no longer be converted to a shared_ptr that
* owns the freed pointer, so you cannot accidentally access the pointed-to
* object after it has been destroyed.
*/
template<typename _Tp>
class weak_ptr : public __weak_ptr<_Tp>
{
template<typename _Arg>
using _Constructible = typename enable_if<
is_constructible<__weak_ptr<_Tp>, _Arg>::value
>::type;
template<typename _Arg>
using _Assignable = typename enable_if<
is_assignable<__weak_ptr<_Tp>&, _Arg>::value, weak_ptr&
>::type;
public:
constexpr weak_ptr() noexcept = default;
template<typename _Yp,
typename = _Constructible<const shared_ptr<_Yp>&>>
weak_ptr(const shared_ptr<_Yp>& __r) noexcept
: __weak_ptr<_Tp>(__r) { }
weak_ptr(const weak_ptr&) noexcept = default;
template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
weak_ptr(const weak_ptr<_Yp>& __r) noexcept
: __weak_ptr<_Tp>(__r) { }
weak_ptr(weak_ptr&&) noexcept = default;
template<typename _Yp, typename = _Constructible<weak_ptr<_Yp>>>
weak_ptr(weak_ptr<_Yp>&& __r) noexcept
: __weak_ptr<_Tp>(std::move(__r)) { }
weak_ptr&
operator=(const weak_ptr& __r) noexcept = default;
template<typename _Yp>
_Assignable<const weak_ptr<_Yp>&>
operator=(const weak_ptr<_Yp>& __r) noexcept
{
this->__weak_ptr<_Tp>::operator=(__r);
return *this;
}
template<typename _Yp>
_Assignable<const shared_ptr<_Yp>&>
operator=(const shared_ptr<_Yp>& __r) noexcept
{
this->__weak_ptr<_Tp>::operator=(__r);
return *this;
}
weak_ptr&
operator=(weak_ptr&& __r) noexcept = default;
template<typename _Yp>
_Assignable<weak_ptr<_Yp>>
operator=(weak_ptr<_Yp>&& __r) noexcept
{
this->__weak_ptr<_Tp>::operator=(std::move(__r));
return *this;
}
shared_ptr<_Tp>
lock() const noexcept
{ return shared_ptr<_Tp>(*this, std::nothrow); }
};
#if __cpp_deduction_guides >= 201606
template<typename _Tp>
weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
#endif
// 20.7.2.3.6 weak_ptr specialized algorithms.
/// Swap overload for weak_ptr
/// @relates weak_ptr
template<typename _Tp>
inline void
swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
{ __a.swap(__b); }
/// Primary template owner_less
template<typename _Tp = void>
struct owner_less;
/// Void specialization of owner_less compares either shared_ptr or weak_ptr
template<>
struct owner_less<void> : _Sp_owner_less<void, void>
{ };
/// Partial specialization of owner_less for shared_ptr.
template<typename _Tp>
struct owner_less<shared_ptr<_Tp>>
: public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
{ };
/// Partial specialization of owner_less for weak_ptr.
template<typename _Tp>
struct owner_less<weak_ptr<_Tp>>
: public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
{ };
/**
* @brief Base class allowing use of member function shared_from_this.
*/
template<typename _Tp>
class enable_shared_from_this
{
protected:
constexpr enable_shared_from_this() noexcept { }
enable_shared_from_this(const enable_shared_from_this&) noexcept { }
enable_shared_from_this&
operator=(const enable_shared_from_this&) noexcept
{ return *this; }
~enable_shared_from_this() { }
public:
shared_ptr<_Tp>
shared_from_this()
{ return shared_ptr<_Tp>(this->_M_weak_this); }
shared_ptr<const _Tp>
shared_from_this() const
{ return shared_ptr<const _Tp>(this->_M_weak_this); }
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
#define __cpp_lib_enable_shared_from_this 201603
weak_ptr<_Tp>
weak_from_this() noexcept
{ return this->_M_weak_this; }
weak_ptr<const _Tp>
weak_from_this() const noexcept
{ return this->_M_weak_this; }
#endif
private:
template<typename _Tp1>
void
_M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
{ _M_weak_this._M_assign(__p, __n); }
// Found by ADL when this is an associated class.
friend const enable_shared_from_this*
__enable_shared_from_this_base(const __shared_count<>&,
const enable_shared_from_this* __p)
{ return __p; }
template<typename, _Lock_policy>
friend class __shared_ptr;
mutable weak_ptr<_Tp> _M_weak_this;
};
/// @relates shared_ptr @{
/**
* @brief Create an object that is owned by a shared_ptr.
* @param __a An allocator.
* @param __args Arguments for the @a _Tp object's constructor.
* @return A shared_ptr that owns the newly created object.
* @throw An exception thrown from @a _Alloc::allocate or from the
* constructor of @a _Tp.
*
* A copy of @a __a will be used to allocate memory for the shared_ptr
* and the new object.
*/
template<typename _Tp, typename _Alloc, typename... _Args>
inline shared_ptr<_Tp>
allocate_shared(const _Alloc& __a, _Args&&... __args)
{
return shared_ptr<_Tp>(_Sp_alloc_shared_tag<_Alloc>{__a},
std::forward<_Args>(__args)...);
}
/**
* @brief Create an object that is owned by a shared_ptr.
* @param __args Arguments for the @a _Tp object's constructor.
* @return A shared_ptr that owns the newly created object.
* @throw std::bad_alloc, or an exception thrown from the
* constructor of @a _Tp.
*/
template<typename _Tp, typename... _Args>
inline shared_ptr<_Tp>
make_shared(_Args&&... __args)
{
typedef typename std::remove_cv<_Tp>::type _Tp_nc;
return std::allocate_shared<_Tp>(std::allocator<_Tp_nc>(),
std::forward<_Args>(__args)...);
}
/// std::hash specialization for shared_ptr.
template<typename _Tp>
struct hash<shared_ptr<_Tp>>
: public __hash_base<size_t, shared_ptr<_Tp>>
{
size_t
operator()(const shared_ptr<_Tp>& __s) const noexcept
{
return std::hash<typename shared_ptr<_Tp>::element_type*>()(__s.get());
}
};
// @} relates shared_ptr
// @} 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
// shared_ptr into a variant.
template<typename _Tp>
struct _Never_valueless_alt<std::shared_ptr<_Tp>>
: std::true_type
{ };
// Provide the strong exception-safety guarantee when emplacing a
// weak_ptr into a variant.
template<typename _Tp>
struct _Never_valueless_alt<std::weak_ptr<_Tp>>
: std::true_type
{ };
} // namespace __detail::__variant
#endif // C++17
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // _SHARED_PTR_H
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