out_ptr.h
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// Smart pointer adaptors -*- C++ -*-
// Copyright The GNU Toolchain Authors.
//
// 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/bits/out_ptr.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{memory}
*/
#ifndef _GLIBCXX_OUT_PTR_H
#define _GLIBCXX_OUT_PTR_H 1
#pragma GCC system_header
#include <bits/version.h>
#ifdef __glibcxx_out_ptr // C++ >= 23
#include <tuple>
#include <bits/ptr_traits.h>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/// Smart pointer adaptor for functions taking an output pointer parameter.
/**
* @tparam _Smart The type of pointer to adapt.
* @tparam _Pointer The type of pointer to convert to.
* @tparam _Args... Argument types used when resetting the smart pointer.
* @since C++23
* @headerfile <memory>
*/
template<typename _Smart, typename _Pointer, typename... _Args>
class out_ptr_t
{
#if _GLIBCXX_HOSTED
static_assert(!__is_shared_ptr<_Smart> || sizeof...(_Args) != 0,
"a deleter must be used when adapting std::shared_ptr "
"with std::out_ptr");
#endif
public:
explicit
out_ptr_t(_Smart& __smart, _Args... __args)
: _M_impl{__smart, std::forward<_Args>(__args)...}
{
if constexpr (requires { _M_impl._M_out_init(); })
_M_impl._M_out_init();
}
out_ptr_t(const out_ptr_t&) = delete;
~out_ptr_t() = default;
operator _Pointer*() const noexcept
{ return _M_impl._M_get(); }
operator void**() const noexcept requires (!same_as<_Pointer, void*>)
{
static_assert(is_pointer_v<_Pointer>);
_Pointer* __p = *this;
return static_cast<void**>(static_cast<void*>(__p));
}
private:
// TODO: Move this to namespace scope? e.g. __detail::_Ptr_adapt_impl
template<typename, typename, typename...>
struct _Impl
{
// This constructor must not modify __s because out_ptr_t and
// inout_ptr_t want to do different things. After construction
// they call _M_out_init() or _M_inout_init() respectively.
_Impl(_Smart& __s, _Args&&... __args)
: _M_smart(__s), _M_args(std::forward<_Args>(__args)...)
{ }
// Called by out_ptr_t to clear the smart pointer before using it.
void
_M_out_init()
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3734. Inconsistency in inout_ptr and out_ptr for empty case
if constexpr (requires { _M_smart.reset(); })
_M_smart.reset();
else
_M_smart = _Smart();
}
// Called by inout_ptr_t to copy the smart pointer's value
// to the pointer that is returned from _M_get().
void
_M_inout_init()
{ _M_ptr = _M_smart.release(); }
// The pointer value returned by operator Pointer*().
_Pointer*
_M_get() const
{ return __builtin_addressof(const_cast<_Pointer&>(_M_ptr)); }
// Finalize the effects on the smart pointer.
~_Impl() noexcept(false);
_Smart& _M_smart;
[[no_unique_address]] _Pointer _M_ptr{};
[[no_unique_address]] tuple<_Args...> _M_args;
};
// Partial specialization for raw pointers.
template<typename _Tp>
struct _Impl<_Tp*, _Tp*>
{
void
_M_out_init()
{ _M_p = nullptr; }
void
_M_inout_init()
{ }
_Tp**
_M_get() const
{ return __builtin_addressof(const_cast<_Tp*&>(_M_p)); }
_Tp*& _M_p;
};
// Partial specialization for raw pointers, with conversion.
template<typename _Tp, typename _Ptr> requires (!is_same_v<_Ptr, _Tp*>)
struct _Impl<_Tp*, _Ptr>
{
explicit
_Impl(_Tp*& __p)
: _M_p(__p)
{ }
void
_M_out_init()
{ _M_p = nullptr; }
void
_M_inout_init()
{ _M_ptr = _M_p; }
_Pointer*
_M_get() const
{ return __builtin_addressof(const_cast<_Pointer&>(_M_ptr)); }
~_Impl() { _M_p = static_cast<_Tp*>(_M_ptr); }
_Tp*& _M_p;
_Pointer _M_ptr{};
};
// Partial specialization for std::unique_ptr.
// This specialization gives direct access to the private member
// of the unique_ptr, avoiding the overhead of storing a separate
// pointer and then resetting the unique_ptr in the destructor.
// FIXME: constrain to only match the primary template,
// not program-defined specializations of unique_ptr.
template<typename _Tp, typename _Del>
struct _Impl<unique_ptr<_Tp, _Del>,
typename unique_ptr<_Tp, _Del>::pointer>
{
void
_M_out_init()
{ _M_smart.reset(); }
_Pointer*
_M_get() const noexcept
{ return __builtin_addressof(_M_smart._M_t._M_ptr()); }
_Smart& _M_smart;
};
// Partial specialization for std::unique_ptr with replacement deleter.
// FIXME: constrain to only match the primary template,
// not program-defined specializations of unique_ptr.
template<typename _Tp, typename _Del, typename _Del2>
struct _Impl<unique_ptr<_Tp, _Del>,
typename unique_ptr<_Tp, _Del>::pointer, _Del2>
{
void
_M_out_init()
{ _M_smart.reset(); }
_Pointer*
_M_get() const noexcept
{ return __builtin_addressof(_M_smart._M_t._M_ptr()); }
~_Impl()
{
if (_M_smart.get())
_M_smart._M_t._M_deleter() = std::forward<_Del2>(_M_del);
}
_Smart& _M_smart;
[[no_unique_address]] _Del2 _M_del;
};
#if _GLIBCXX_HOSTED
// Partial specialization for std::shared_ptr.
// This specialization gives direct access to the private member
// of the shared_ptr, avoiding the overhead of storing a separate
// pointer and then resetting the shared_ptr in the destructor.
// A new control block is allocated in the constructor, so that if
// allocation fails it doesn't throw an exception from the destructor.
template<typename _Tp, typename _Del, typename _Alloc>
requires (is_base_of_v<__shared_ptr<_Tp>, shared_ptr<_Tp>>)
struct _Impl<shared_ptr<_Tp>,
typename shared_ptr<_Tp>::element_type*, _Del, _Alloc>
{
_Impl(_Smart& __s, _Del __d, _Alloc __a = _Alloc())
: _M_smart(__s)
{
// We know shared_ptr cannot be used with inout_ptr_t
// so we can do all set up here, instead of in _M_out_init().
_M_smart.reset();
// Similar to the shared_ptr(Y*, D, A) constructor, except that if
// the allocation throws we do not need (or want) to call deleter.
typename _Scd::__allocator_type __a2(__a);
auto __mem = __a2.allocate(1);
::new (__mem) _Scd(nullptr, std::forward<_Del>(__d),
std::forward<_Alloc>(__a));
_M_smart._M_refcount._M_pi = __mem;
}
_Pointer*
_M_get() const noexcept
{ return __builtin_addressof(_M_smart._M_ptr); }
~_Impl()
{
auto& __pi = _M_smart._M_refcount._M_pi;
if (_Sp __ptr = _M_smart.get())
static_cast<_Scd*>(__pi)->_M_impl._M_ptr = __ptr;
else // Destroy the control block manually without invoking deleter.
std::__exchange(__pi, nullptr)->_M_destroy();
}
_Smart& _M_smart;
using _Sp = typename _Smart::element_type*;
using _Scd = _Sp_counted_deleter<_Sp, decay_t<_Del>,
remove_cvref_t<_Alloc>,
__default_lock_policy>;
};
// Partial specialization for std::shared_ptr, without custom allocator.
template<typename _Tp, typename _Del>
requires (is_base_of_v<__shared_ptr<_Tp>, shared_ptr<_Tp>>)
struct _Impl<shared_ptr<_Tp>,
typename shared_ptr<_Tp>::element_type*, _Del>
: _Impl<_Smart, _Pointer, _Del, allocator<void>>
{
using _Impl<_Smart, _Pointer, _Del, allocator<void>>::_Impl;
};
#endif
using _Impl_t = _Impl<_Smart, _Pointer, _Args...>;
_Impl_t _M_impl;
template<typename, typename, typename...> friend class inout_ptr_t;
};
/// Smart pointer adaptor for functions taking an inout pointer parameter.
/**
* @tparam _Smart The type of pointer to adapt.
* @tparam _Pointer The type of pointer to convert to.
* @tparam _Args... Argument types used when resetting the smart pointer.
* @since C++23
* @headerfile <memory>
*/
template<typename _Smart, typename _Pointer, typename... _Args>
class inout_ptr_t
{
#if _GLIBCXX_HOSTED
static_assert(!__is_shared_ptr<_Smart>,
"std::inout_ptr can not be used to wrap std::shared_ptr");
#endif
public:
explicit
inout_ptr_t(_Smart& __smart, _Args... __args)
: _M_impl{__smart, std::forward<_Args>(__args)...}
{
if constexpr (requires { _M_impl._M_inout_init(); })
_M_impl._M_inout_init();
}
inout_ptr_t(const inout_ptr_t&) = delete;
~inout_ptr_t() = default;
operator _Pointer*() const noexcept
{ return _M_impl._M_get(); }
operator void**() const noexcept requires (!same_as<_Pointer, void*>)
{
static_assert(is_pointer_v<_Pointer>);
_Pointer* __p = *this;
return static_cast<void**>(static_cast<void*>(__p));
}
private:
#if _GLIBCXX_HOSTED
// Avoid an invalid instantiation of out_ptr_t<shared_ptr<T>, ...>
using _Out_ptr_t
= __conditional_t<__is_shared_ptr<_Smart>,
out_ptr_t<void*, void*>,
out_ptr_t<_Smart, _Pointer, _Args...>>;
#else
using _Out_ptr_t = out_ptr_t<_Smart, _Pointer, _Args...>;
#endif
using _Impl_t = typename _Out_ptr_t::_Impl_t;
_Impl_t _M_impl;
};
/// @cond undocumented
namespace __detail
{
// POINTER_OF metafunction
template<typename _Tp>
consteval auto
__pointer_of()
{
if constexpr (requires { typename _Tp::pointer; })
return type_identity<typename _Tp::pointer>{};
else if constexpr (requires { typename _Tp::element_type; })
return type_identity<typename _Tp::element_type*>{};
else
{
using _Traits = pointer_traits<_Tp>;
if constexpr (requires { typename _Traits::element_type; })
return type_identity<typename _Traits::element_type*>{};
}
// else POINTER_OF(S) is not a valid type, return void.
}
// POINTER_OF_OR metafunction
template<typename _Smart, typename _Ptr>
consteval auto
__pointer_of_or()
{
using _TypeId = decltype(__detail::__pointer_of<_Smart>());
if constexpr (is_void_v<_TypeId>)
return type_identity<_Ptr>{};
else
return _TypeId{};
}
// Returns Pointer if !is_void_v<Pointer>, otherwise POINTER_OF(Smart).
template<typename _Ptr, typename _Smart>
consteval auto
__choose_ptr()
{
if constexpr (!is_void_v<_Ptr>)
return type_identity<_Ptr>{};
else
return __detail::__pointer_of<_Smart>();
}
template<typename _Smart, typename _Sp, typename... _Args>
concept __resettable = requires (_Smart& __s) {
__s.reset(std::declval<_Sp>(), std::declval<_Args>()...);
};
}
/// @endcond
/// Adapt a smart pointer for functions taking an output pointer parameter.
/**
* @tparam _Pointer The type of pointer to convert to.
* @param __s The pointer that should take ownership of the result.
* @param __args... Arguments to use when resetting the smart pointer.
* @return A `std::out_ptr_t` referring to `__s`.
* @since C++23
* @headerfile <memory>
*/
template<typename _Pointer = void, typename _Smart, typename... _Args>
inline auto
out_ptr(_Smart& __s, _Args&&... __args)
{
using _TypeId = decltype(__detail::__choose_ptr<_Pointer, _Smart>());
static_assert(!is_void_v<_TypeId>, "first argument to std::out_ptr "
"must be a pointer-like type");
using _Ret = out_ptr_t<_Smart, typename _TypeId::type, _Args&&...>;
return _Ret(__s, std::forward<_Args>(__args)...);
}
/// Adapt a smart pointer for functions taking an inout pointer parameter.
/**
* @tparam _Pointer The type of pointer to convert to.
* @param __s The pointer that should take ownership of the result.
* @param __args... Arguments to use when resetting the smart pointer.
* @return A `std::inout_ptr_t` referring to `__s`.
* @since C++23
* @headerfile <memory>
*/
template<typename _Pointer = void, typename _Smart, typename... _Args>
inline auto
inout_ptr(_Smart& __s, _Args&&... __args)
{
using _TypeId = decltype(__detail::__choose_ptr<_Pointer, _Smart>());
static_assert(!is_void_v<_TypeId>, "first argument to std::inout_ptr "
"must be a pointer-like type");
using _Ret = inout_ptr_t<_Smart, typename _TypeId::type, _Args&&...>;
return _Ret(__s, std::forward<_Args>(__args)...);
}
/// @cond undocumented
template<typename _Smart, typename _Pointer, typename... _Args>
template<typename _Smart2, typename _Pointer2, typename... _Args2>
inline
out_ptr_t<_Smart, _Pointer, _Args...>::
_Impl<_Smart2, _Pointer2, _Args2...>::~_Impl()
{
using _TypeId = decltype(__detail::__pointer_of_or<_Smart, _Pointer>());
using _Sp = typename _TypeId::type;
if (!_M_ptr)
return;
_Smart& __s = _M_smart;
_Pointer& __p = _M_ptr;
auto __reset = [&](auto&&... __args) {
if constexpr (__detail::__resettable<_Smart, _Sp, _Args...>)
__s.reset(static_cast<_Sp>(__p), std::forward<_Args>(__args)...);
else if constexpr (is_constructible_v<_Smart, _Sp, _Args...>)
__s = _Smart(static_cast<_Sp>(__p), std::forward<_Args>(__args)...);
else
static_assert(is_constructible_v<_Smart, _Sp, _Args...>);
};
if constexpr (sizeof...(_Args) >= 2)
std::apply(__reset, std::move(_M_args));
else if constexpr (sizeof...(_Args) == 1)
__reset(std::get<0>(std::move(_M_args)));
else
__reset();
}
/// @endcond
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // __glibcxx_out_ptr
#endif /* _GLIBCXX_OUT_PTR_H */
tuple
version.h
ptr_traits.h
std::declval
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition type_traits:2483
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:137
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:71
std
ISO C++ entities toplevel namespace is std.
std::__detail
Implementation details not part of the namespace std interface.