libcxx/include/__ranges/counted.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___RANGES_COUNTED_H
  11 #define _LIBCPP___RANGES_COUNTED_H
  12
  13 #include <__concepts/convertible_to.h>
  14 #include <__config>
  15 #include <__cstddef/size_t.h>
  16 #include <__iterator/concepts.h>
  17 #include <__iterator/counted_iterator.h>
  18 #include <__iterator/default_sentinel.h>
  19 #include <__iterator/incrementable_traits.h>
  20 #include <__iterator/iterator_traits.h>
  21 #include <__memory/pointer_traits.h>
  22 #include <__ranges/subrange.h>
  23 #include <__type_traits/decay.h>
  24 #include <__utility/forward.h>
  25 #include <__utility/move.h>
  26 #include <span>
  27
  28 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  29 #  pragma GCC system_header
  30 #endif
  31
  32 _LIBCPP_PUSH_MACROS
  33 #include <__undef_macros>
  34
  35 _LIBCPP_BEGIN_NAMESPACE_STD
  36
  37 #if _LIBCPP_STD_VER >= 20
  38
  39 namespace ranges::views {
  40
  41 namespace __counted {
  42
  43 struct __fn {
  44   template <contiguous_iterator _It>
  45   _LIBCPP_HIDE_FROM_ABI static constexpr auto
  46   __go(_It __it,
  47        iter_difference_t<_It> __count) noexcept(noexcept(span(std::to_address(__it), static_cast<size_t>(__count))))
  48   // Deliberately omit return-type SFINAE, because to_address is not SFINAE-friendly
  49   {
  50     return span(std::to_address(__it), static_cast<size_t>(__count));
  51   }
  52
  53   template <random_access_iterator _It>
  54   _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_It __it, iter_difference_t<_It> __count) noexcept(
  55       noexcept(subrange(__it, __it + __count))) -> decltype(subrange(__it, __it + __count)) {
  56     return subrange(__it, __it + __count);
  57   }
  58
  59   template <class _It>
  60   _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_It __it, iter_difference_t<_It> __count) noexcept(
  61       noexcept(subrange(counted_iterator(std::move(__it), __count), default_sentinel)))
  62       -> decltype(subrange(counted_iterator(std::move(__it), __count), default_sentinel)) {
  63     return subrange(counted_iterator(std::move(__it), __count), default_sentinel);
  64   }
  65
  66   template <class _It, convertible_to<iter_difference_t<_It>> _Diff>
  67     requires input_or_output_iterator<decay_t<_It>>
  68   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_It&& __it, _Diff&& __count) const
  69       noexcept(noexcept(__go(std::forward<_It>(__it), std::forward<_Diff>(__count))))
  70           -> decltype(__go(std::forward<_It>(__it), std::forward<_Diff>(__count))) {
  71     return __go(std::forward<_It>(__it), std::forward<_Diff>(__count));
  72   }
  73 };
  74
  75 } // namespace __counted
  76
  77 inline namespace __cpo {
  78 inline constexpr auto counted = __counted::__fn{};
  79 } // namespace __cpo
  80
  81 } // namespace ranges::views
  82
  83 #endif // _LIBCPP_STD_VER >= 20
  84
  85 _LIBCPP_END_NAMESPACE_STD
  86
  87 _LIBCPP_POP_MACROS
  88
  89 #endif // _LIBCPP___RANGES_COUNTED_H