libcxx/include/__ranges/counted.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// 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___RANGES_COUNTED_H
#define _LIBCPP___RANGES_COUNTED_H

#include <__concepts/convertible_to.h>
#include <__config>
#include <__iterator/concepts.h>
#include <__iterator/counted_iterator.h>
#include <__iterator/default_sentinel.h>
#include <__iterator/incrementable_traits.h>
#include <__iterator/iterator_traits.h>
#include <__memory/pointer_traits.h>
#include <__ranges/subrange.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <span>
#include <type_traits>

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

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER > 17

namespace ranges::views {

namespace __counted {

  struct __fn {
    template<contiguous_iterator _It>
    _LIBCPP_HIDE_FROM_ABI
    static constexpr auto __go(_It __it, iter_difference_t<_It> __count)
      noexcept(noexcept(span(std::to_address(__it), static_cast<size_t>(__count))))
      // Deliberately omit return-type SFINAE, because to_address is not SFINAE-friendly
      { return          span(std::to_address(__it), static_cast<size_t>(__count)); }

    template<random_access_iterator _It>
    _LIBCPP_HIDE_FROM_ABI
    static constexpr auto __go(_It __it, iter_difference_t<_It> __count)
      noexcept(noexcept(subrange(__it, __it + __count)))
      -> decltype(      subrange(__it, __it + __count))
      { return          subrange(__it, __it + __count); }

    template<class _It>
    _LIBCPP_HIDE_FROM_ABI
    static constexpr auto __go(_It __it, iter_difference_t<_It> __count)
      noexcept(noexcept(subrange(counted_iterator(std::move(__it), __count), default_sentinel)))
      -> decltype(      subrange(counted_iterator(std::move(__it), __count), default_sentinel))
      { return          subrange(counted_iterator(std::move(__it), __count), default_sentinel); }

    template<class _It, convertible_to<iter_difference_t<_It>> _Diff>
      requires input_or_output_iterator<decay_t<_It>>
    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
    constexpr auto operator()(_It&& __it, _Diff&& __count) const
      noexcept(noexcept(__go(std::forward<_It>(__it), std::forward<_Diff>(__count))))
      -> decltype(      __go(std::forward<_It>(__it), std::forward<_Diff>(__count)))
      { return          __go(std::forward<_It>(__it), std::forward<_Diff>(__count)); }
  };

} // namespace __counted

inline namespace __cpo {
  inline constexpr auto counted = __counted::__fn{};
} // namespace __cpo

} // namespace ranges::views

#endif // _LIBCPP_STD_VER > 17

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___RANGES_COUNTED_H