include/__tuple/find_index.h

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___TUPLE_FIND_INDEX_H
#define _LIBCPP___TUPLE_FIND_INDEX_H

#include <__config>
#include <__type_traits/is_same.h>
#include <cstddef>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

#if _LIBCPP_STD_VER >= 14

_LIBCPP_BEGIN_NAMESPACE_STD

namespace __find_detail {

static constexpr size_t __not_found = static_cast<size_t>(-1);
static constexpr size_t __ambiguous = __not_found - 1;

inline _LIBCPP_HIDE_FROM_ABI constexpr size_t __find_idx_return(size_t __curr_i, size_t __res, bool __matches) {
  return !__matches ? __res : (__res == __not_found ? __curr_i : __ambiguous);
}

template <size_t _Nx>
inline _LIBCPP_HIDE_FROM_ABI constexpr size_t __find_idx(size_t __i, const bool (&__matches)[_Nx]) {
  return __i == _Nx
           ? __not_found
           : __find_detail::__find_idx_return(__i, __find_detail::__find_idx(__i + 1, __matches), __matches[__i]);
}

template <class _T1, class... _Args>
struct __find_exactly_one_checked {
  static constexpr bool __matches[sizeof...(_Args)] = {is_same<_T1, _Args>::value...};
  static constexpr size_t value                     = __find_detail::__find_idx(0, __matches);
  static_assert(value != __not_found, "type not found in type list");
  static_assert(value != __ambiguous, "type occurs more than once in type list");
};

template <class _T1>
struct __find_exactly_one_checked<_T1> {
  static_assert(!is_same<_T1, _T1>::value, "type not in empty type list");
};

} // namespace __find_detail

template <typename _T1, typename... _Args>
struct __find_exactly_one_t : public __find_detail::__find_exactly_one_checked<_T1, _Args...> {};

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_STD_VER >= 14

#endif // _LIBCPP___TUPLE_FIND_INDEX_H