ptr_traits.h
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// Pointer Traits -*- C++ -*-
// Copyright (C) 2011-2022 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/ptr_traits.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{memory}
*/
#ifndef _PTR_TRAITS_H
#define _PTR_TRAITS_H 1
#if __cplusplus >= 201103L
#include <bits/move.h>
#if __cplusplus > 201703L
#include <concepts>
# ifndef __cpp_lib_constexpr_memory
// Defined to a newer value in bits/unique_ptr.h for C++23
# define __cpp_lib_constexpr_memory 201811L
# endif
namespace __gnu_debug { struct _Safe_iterator_base; }
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
class __undefined;
// For a specialization `SomeTemplate<T, Types...>` the member `type` is T,
// otherwise `type` is `__undefined`.
template<typename _Tp>
struct __get_first_arg
{ using type = __undefined; };
template<template<typename, typename...> class _SomeTemplate, typename _Tp,
typename... _Types>
struct __get_first_arg<_SomeTemplate<_Tp, _Types...>>
{ using type = _Tp; };
// For a specialization `SomeTemplate<T, Args...>` and a type `U` the member
// `type` is `SomeTemplate<U, Args...>`, otherwise there is no member `type`.
template<typename _Tp, typename _Up>
struct __replace_first_arg
{ };
template<template<typename, typename...> class _SomeTemplate, typename _Up,
typename _Tp, typename... _Types>
struct __replace_first_arg<_SomeTemplate<_Tp, _Types...>, _Up>
{ using type = _SomeTemplate<_Up, _Types...>; };
#if __cpp_concepts
// When concepts are supported detection of _Ptr::element_type is done
// by a requires-clause, so __ptr_traits_elem_t only needs to do this:
template<typename _Ptr>
using __ptr_traits_elem_t = typename __get_first_arg<_Ptr>::type;
#else
// Detect the element type of a pointer-like type.
template<typename _Ptr, typename = void>
struct __ptr_traits_elem : __get_first_arg<_Ptr>
{ };
// Use _Ptr::element_type if is a valid type.
template<typename _Ptr>
struct __ptr_traits_elem<_Ptr, __void_t<typename _Ptr::element_type>>
{ using type = typename _Ptr::element_type; };
template<typename _Ptr>
using __ptr_traits_elem_t = typename __ptr_traits_elem<_Ptr>::type;
#endif
// Define pointer_traits<P>::pointer_to.
template<typename _Ptr, typename _Elt, bool = is_void<_Elt>::value>
struct __ptr_traits_ptr_to
{
using pointer = _Ptr;
using element_type = _Elt;
/**
* @brief Obtain a pointer to an object
* @param __r A reference to an object of type `element_type`
* @return `pointer::pointer_to(__e)`
* @pre `pointer::pointer_to(__e)` is a valid expression.
*/
static pointer
pointer_to(element_type& __e)
#if __cpp_lib_concepts
requires requires {
{ pointer::pointer_to(__e) } -> convertible_to<pointer>;
}
#endif
{ return pointer::pointer_to(__e); }
};
// Do not define pointer_traits<P>::pointer_to if element type is void.
template<typename _Ptr, typename _Elt>
struct __ptr_traits_ptr_to<_Ptr, _Elt, true>
{ };
// Partial specialization defining pointer_traits<T*>::pointer_to(T&).
template<typename _Tp>
struct __ptr_traits_ptr_to<_Tp*, _Tp, false>
{
using pointer = _Tp*;
using element_type = _Tp;
/**
* @brief Obtain a pointer to an object
* @param __r A reference to an object of type `element_type`
* @return `addressof(__r)`
*/
static _GLIBCXX20_CONSTEXPR pointer
pointer_to(element_type& __r) noexcept
{ return std::addressof(__r); }
};
template<typename _Ptr, typename _Elt>
struct __ptr_traits_impl : __ptr_traits_ptr_to<_Ptr, _Elt>
{
private:
template<typename _Tp, typename = void>
struct __difference { using type = ptrdiff_t; };
template<typename _Tp>
#if __cpp_concepts
requires requires { typename _Tp::difference_type; }
struct __difference<_Tp>
#else
struct __difference<_Tp, __void_t<typename _Tp::difference_type>>
#endif
{ using type = typename _Tp::difference_type; };
template<typename _Tp, typename _Up, typename = void>
struct __rebind : __replace_first_arg<_Tp, _Up> { };
template<typename _Tp, typename _Up>
#if __cpp_concepts
requires requires { typename _Tp::template rebind<_Up>; }
struct __rebind<_Tp, _Up>
#else
struct __rebind<_Tp, _Up, __void_t<typename _Tp::template rebind<_Up>>>
#endif
{ using type = typename _Tp::template rebind<_Up>; };
public:
/// The pointer type.
using pointer = _Ptr;
/// The type pointed to.
using element_type = _Elt;
/// The type used to represent the difference between two pointers.
using difference_type = typename __difference<_Ptr>::type;
/// A pointer to a different type.
template<typename _Up>
using rebind = typename __rebind<_Ptr, _Up>::type;
};
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3545. std::pointer_traits should be SFINAE-friendly
template<typename _Ptr>
struct __ptr_traits_impl<_Ptr, __undefined>
{ };
/**
* @brief Uniform interface to all pointer-like types
* @ingroup pointer_abstractions
* @since C++11
*/
template<typename _Ptr>
struct pointer_traits : __ptr_traits_impl<_Ptr, __ptr_traits_elem_t<_Ptr>>
{ };
#if __cpp_concepts
template<typename _Ptr> requires requires { typename _Ptr::element_type; }
struct pointer_traits<_Ptr>
: __ptr_traits_impl<_Ptr, typename _Ptr::element_type>
{ };
#endif
/**
* @brief Partial specialization for built-in pointers.
* @ingroup pointer_abstractions
* @since C++11
*/
template<typename _Tp>
struct pointer_traits<_Tp*> : __ptr_traits_ptr_to<_Tp*, _Tp>
{
/// The pointer type
typedef _Tp* pointer;
/// The type pointed to
typedef _Tp element_type;
/// Type used to represent the difference between two pointers
typedef ptrdiff_t difference_type;
/// A pointer to a different type.
template<typename _Up> using rebind = _Up*;
};
/// Convenience alias for rebinding pointers.
template<typename _Ptr, typename _Tp>
using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
template<typename _Tp>
constexpr _Tp*
__to_address(_Tp* __ptr) noexcept
{
static_assert(!std::is_function<_Tp>::value, "not a function pointer");
return __ptr;
}
#if __cplusplus <= 201703L
template<typename _Ptr>
constexpr typename std::pointer_traits<_Ptr>::element_type*
__to_address(const _Ptr& __ptr)
{ return std::__to_address(__ptr.operator->()); }
#else
template<typename _Ptr>
constexpr auto
__to_address(const _Ptr& __ptr) noexcept
-> decltype(std::pointer_traits<_Ptr>::to_address(__ptr))
{ return std::pointer_traits<_Ptr>::to_address(__ptr); }
template<typename _Ptr, typename... _None>
constexpr auto
__to_address(const _Ptr& __ptr, _None...) noexcept
{
if constexpr (is_base_of_v<__gnu_debug::_Safe_iterator_base, _Ptr>)
return std::__to_address(__ptr.base().operator->());
else
return std::__to_address(__ptr.operator->());
}
#define __cpp_lib_to_address 201711L
/**
* @brief Obtain address referenced by a pointer to an object
* @param __ptr A pointer to an object
* @return @c __ptr
* @ingroup pointer_abstractions
*/
template<typename _Tp>
constexpr _Tp*
to_address(_Tp* __ptr) noexcept
{ return std::__to_address(__ptr); }
/**
* @brief Obtain address referenced by a pointer to an object
* @param __ptr A pointer to an object
* @return @c pointer_traits<_Ptr>::to_address(__ptr) if that expression is
well-formed, otherwise @c to_address(__ptr.operator->())
* @ingroup pointer_abstractions
*/
template<typename _Ptr>
constexpr auto
to_address(const _Ptr& __ptr) noexcept
{ return std::__to_address(__ptr); }
#endif // C++2a
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif
#endif
concepts
move.h
std::to_address
constexpr auto to_address(const _Ptr &__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition: ptr_traits.h:278
std::to_address
constexpr _Tp * to_address(_Tp *__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition: ptr_traits.h:266
std::addressof
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition: move.h:145
std
ISO C++ entities toplevel namespace is std.
std::__ptr_rebind
typename pointer_traits< _Ptr >::template rebind< _Tp > __ptr_rebind
Convenience alias for rebinding pointers.
Definition: ptr_traits.h:224
__gnu_debug
GNU debug classes for public use.
Definition: boost_concept_check.h:58
std::is_function
is_function
Definition: type_traits:541
std::pointer_traits
Uniform interface to all pointer-like types.
Definition: ptr_traits.h:195
std::pointer_traits< _Tp * >::pointer
_Tp * pointer
The pointer type.
Definition: ptr_traits.h:213
std::pointer_traits< _Tp * >::difference_type
ptrdiff_t difference_type
Type used to represent the difference between two pointers.
Definition: ptr_traits.h:217
std::pointer_traits< _Tp * >::element_type
_Tp element_type
The type pointed to.
Definition: ptr_traits.h:215
std::pointer_traits< _Tp * >::rebind
_Up * rebind
A pointer to a different type.
Definition: ptr_traits.h:219