libcxx/include/__tuple/tuple_element.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___TUPLE_TUPLE_ELEMENT_H
  10 #define _LIBCPP___TUPLE_TUPLE_ELEMENT_H
  11
  12 #include <__config>
  13 #include <__tuple/tuple_indices.h>
  14 #include <__tuple/tuple_types.h>
  15 #include <__type_traits/add_const.h>
  16 #include <__type_traits/add_cv.h>
  17 #include <__type_traits/add_volatile.h>
  18 #include <cstddef>
  19
  20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  21 #  pragma GCC system_header
  22 #endif
  23
  24 _LIBCPP_BEGIN_NAMESPACE_STD
  25
  26 template <size_t _Ip, class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_element;
  27
  28 template <size_t _Ip, class _Tp>
  29 struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, const _Tp>
  30 {
  31     typedef _LIBCPP_NODEBUG typename add_const<typename tuple_element<_Ip, _Tp>::type>::type type;
  32 };
  33
  34 template <size_t _Ip, class _Tp>
  35 struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, volatile _Tp>
  36 {
  37     typedef _LIBCPP_NODEBUG typename add_volatile<typename tuple_element<_Ip, _Tp>::type>::type type;
  38 };
  39
  40 template <size_t _Ip, class _Tp>
  41 struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, const volatile _Tp>
  42 {
  43     typedef _LIBCPP_NODEBUG typename add_cv<typename tuple_element<_Ip, _Tp>::type>::type type;
  44 };
  45
  46 #ifndef _LIBCPP_CXX03_LANG
  47
  48 #if !__has_builtin(__type_pack_element)
  49
  50 namespace __indexer_detail {
  51
  52 template <size_t _Idx, class _Tp>
  53 struct __indexed { using type _LIBCPP_NODEBUG = _Tp; };
  54
  55 template <class _Types, class _Indexes> struct __indexer;
  56
  57 template <class ..._Types, size_t ..._Idx>
  58 struct __indexer<__tuple_types<_Types...>, __tuple_indices<_Idx...>>
  59     : __indexed<_Idx, _Types>...
  60 {};
  61
  62 template <size_t _Idx, class _Tp>
  63 __indexed<_Idx, _Tp> __at_index(__indexed<_Idx, _Tp> const&);
  64
  65 } // namespace __indexer_detail
  66
  67 template <size_t _Idx, class ..._Types>
  68 using __type_pack_element _LIBCPP_NODEBUG = typename decltype(
  69     __indexer_detail::__at_index<_Idx>(
  70         __indexer_detail::__indexer<
  71             __tuple_types<_Types...>,
  72             typename __make_tuple_indices<sizeof...(_Types)>::type
  73         >{})
  74   )::type;
  75 #endif
  76
  77 template <size_t _Ip, class ..._Types>
  78 struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, __tuple_types<_Types...> >
  79 {
  80     static_assert(_Ip < sizeof...(_Types), "tuple_element index out of range");
  81     typedef _LIBCPP_NODEBUG __type_pack_element<_Ip, _Types...> type;
  82 };
  83
  84 #if _LIBCPP_STD_VER >= 14
  85 template <size_t _Ip, class ..._Tp>
  86 using tuple_element_t _LIBCPP_NODEBUG = typename tuple_element <_Ip, _Tp...>::type;
  87 #endif
  88
  89 #endif // _LIBCPP_CXX03_LANG
  90
  91 _LIBCPP_END_NAMESPACE_STD
  92
  93 #endif // _LIBCPP___TUPLE_TUPLE_ELEMENT_H