libcxx/include/__cxx03/__tuple/find_index.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___CXX03___TUPLE_FIND_INDEX_H
  10 #define _LIBCPP___CXX03___TUPLE_FIND_INDEX_H
  11
  12 #include <__cxx03/__config>
  13 #include <__cxx03/__type_traits/is_same.h>
  14 #include <__cxx03/cstddef>
  15
  16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  17 #  pragma GCC system_header
  18 #endif
  19
  20 #if _LIBCPP_STD_VER >= 14
  21
  22 _LIBCPP_BEGIN_NAMESPACE_STD
  23
  24 namespace __find_detail {
  25
  26 static constexpr size_t __not_found = static_cast<size_t>(-1);
  27 static constexpr size_t __ambiguous = __not_found - 1;
  28
  29 inline _LIBCPP_HIDE_FROM_ABI constexpr size_t __find_idx_return(size_t __curr_i, size_t __res, bool __matches) {
  30   return !__matches ? __res : (__res == __not_found ? __curr_i : __ambiguous);
  31 }
  32
  33 template <size_t _Nx>
  34 inline _LIBCPP_HIDE_FROM_ABI constexpr size_t __find_idx(size_t __i, const bool (&__matches)[_Nx]) {
  35   return __i == _Nx
  36            ? __not_found
  37            : __find_detail::__find_idx_return(__i, __find_detail::__find_idx(__i + 1, __matches), __matches[__i]);
  38 }
  39
  40 template <class _T1, class... _Args>
  41 struct __find_exactly_one_checked {
  42   static constexpr bool __matches[sizeof...(_Args)] = {is_same<_T1, _Args>::value...};
  43   static constexpr size_t value                     = __find_detail::__find_idx(0, __matches);
  44   static_assert(value != __not_found, "type not found in type list");
  45   static_assert(value != __ambiguous, "type occurs more than once in type list");
  46 };
  47
  48 template <class _T1>
  49 struct __find_exactly_one_checked<_T1> {
  50   static_assert(!is_same<_T1, _T1>::value, "type not in empty type list");
  51 };
  52
  53 } // namespace __find_detail
  54
  55 template <typename _T1, typename... _Args>
  56 struct __find_exactly_one_t : public __find_detail::__find_exactly_one_checked<_T1, _Args...> {};
  57
  58 _LIBCPP_END_NAMESPACE_STD
  59
  60 #endif // _LIBCPP_STD_VER >= 14
  61
  62 #endif // _LIBCPP___CXX03___TUPLE_FIND_INDEX_H