libstdc++
ptr_traits.h
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00001 // Pointer Traits -*- C++ -*-
00002 
00003 // Copyright (C) 2011-2016 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file bits/ptr_traits.h
00026  *  This is an internal header file, included by other library headers.
00027  *  Do not attempt to use it directly. @headername{memory}
00028  */
00029 
00030 #ifndef _PTR_TRAITS_H
00031 #define _PTR_TRAITS_H 1
00032 
00033 #if __cplusplus >= 201103L
00034 
00035 #include <bits/move.h>
00036 
00037 namespace std _GLIBCXX_VISIBILITY(default)
00038 {
00039 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00040 
00041   class __undefined;
00042 
00043   // Given Template<T, ...> return T, otherwise invalid.
00044   template<typename _Tp>
00045     struct __get_first_arg
00046     { using type = __undefined; };
00047 
00048   template<template<typename, typename...> class _Template, typename _Tp,
00049            typename... _Types>
00050     struct __get_first_arg<_Template<_Tp, _Types...>>
00051     { using type = _Tp; };
00052 
00053   template<typename _Tp>
00054     using __get_first_arg_t = typename __get_first_arg<_Tp>::type;
00055 
00056   // Given Template<T, ...> and U return Template<U, ...>, otherwise invalid.
00057   template<typename _Tp, typename _Up>
00058     struct __replace_first_arg
00059     { using type = __undefined; };
00060 
00061   template<template<typename, typename...> class _Template, typename _Up,
00062            typename _Tp, typename... _Types>
00063     struct __replace_first_arg<_Template<_Tp, _Types...>, _Up>
00064     { using type = _Template<_Up, _Types...>; };
00065 
00066   template<typename _Tp, typename _Up>
00067     using __replace_first_arg_t = typename __replace_first_arg<_Tp, _Up>::type;
00068 
00069   template<typename _Tp>
00070     using __make_not_void
00071       = typename conditional<is_void<_Tp>::value, __undefined, _Tp>::type;
00072 
00073   /**
00074    * @brief  Uniform interface to all pointer-like types
00075    * @ingroup pointer_abstractions
00076   */
00077   template<typename _Ptr>
00078     struct pointer_traits
00079     {
00080     private:
00081       template<typename _Tp>
00082         using __element_type = typename _Tp::element_type;
00083 
00084       template<typename _Tp>
00085         using __difference_type = typename _Tp::difference_type;
00086 
00087       template<typename _Tp, typename _Up>
00088         using __rebind = typename _Tp::template rebind<_Up>;
00089 
00090     public:
00091       /// The pointer type.
00092       using pointer = _Ptr;
00093 
00094       /// The type pointed to.
00095       using element_type
00096         = __detected_or_t_<__get_first_arg_t, __element_type, _Ptr>;
00097 
00098       /// The type used to represent the difference between two pointers.
00099       using difference_type
00100         = __detected_or_t<ptrdiff_t, __difference_type, _Ptr>;
00101 
00102       /// A pointer to a different type.
00103       template<typename _Up>
00104         using rebind
00105           = __detected_or_t_<__replace_first_arg_t, __rebind, _Ptr, _Up>;
00106 
00107       static _Ptr
00108       pointer_to(__make_not_void<element_type>& __e)
00109       { return _Ptr::pointer_to(__e); }
00110 
00111       static_assert(!is_same<element_type, __undefined>::value,
00112           "pointer type defines element_type or is like SomePointer<T, Args>");
00113       static_assert(!is_same<rebind<element_type>, __undefined>::value,
00114           "pointer type defines rebind<U> or is like SomePointer<T, Args>");
00115     };
00116 
00117   /**
00118    * @brief  Partial specialization for built-in pointers.
00119    * @ingroup pointer_abstractions
00120   */
00121   template<typename _Tp>
00122     struct pointer_traits<_Tp*>
00123     {
00124       /// The pointer type
00125       typedef _Tp* pointer;
00126       /// The type pointed to
00127       typedef _Tp  element_type;
00128       /// Type used to represent the difference between two pointers
00129       typedef ptrdiff_t difference_type;
00130 
00131       template<typename _Up>
00132         using rebind = _Up*;
00133 
00134       /**
00135        *  @brief  Obtain a pointer to an object
00136        *  @param  __r  A reference to an object of type @c element_type
00137        *  @return @c addressof(__r)
00138       */
00139       static pointer
00140       pointer_to(__make_not_void<element_type>& __r) noexcept
00141       { return std::addressof(__r); }
00142     };
00143 
00144   /// Convenience alias for rebinding pointers.
00145   template<typename _Ptr, typename _Tp>
00146     using __ptr_rebind = typename pointer_traits<_Ptr>::template rebind<_Tp>;
00147 
00148 _GLIBCXX_END_NAMESPACE_VERSION
00149 } // namespace std
00150 
00151 #endif
00152 
00153 #endif