libcxx/include/__iterator/projected.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___ITERATOR_PROJECTED_H
  11 #define _LIBCPP___ITERATOR_PROJECTED_H
  12
  13 #include <__config>
  14 #include <__iterator/concepts.h>
  15 #include <__iterator/incrementable_traits.h> // iter_difference_t
  16 #include <__type_traits/remove_cvref.h>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_BEGIN_NAMESPACE_STD
  23
  24 #if _LIBCPP_STD_VER >= 20
  25
  26 template <class _It, class _Proj>
  27 struct __projected_impl {
  28   struct __type {
  29     using __primary_template     = __type;
  30     using __projected_iterator   = _It;
  31     using __projected_projection = _Proj;
  32
  33     using value_type = remove_cvref_t<indirect_result_t<_Proj&, _It>>;
  34     indirect_result_t<_Proj&, _It> operator*() const; // not defined
  35   };
  36 };
  37
  38 template <weakly_incrementable _It, class _Proj>
  39 struct __projected_impl<_It, _Proj> {
  40   struct __type {
  41     using __primary_template     = __type;
  42     using __projected_iterator   = _It;
  43     using __projected_projection = _Proj;
  44
  45     using value_type      = remove_cvref_t<indirect_result_t<_Proj&, _It>>;
  46     using difference_type = iter_difference_t<_It>;
  47     indirect_result_t<_Proj&, _It> operator*() const; // not defined
  48   };
  49 };
  50
  51 // Note that we implement std::projected in a way that satisfies P2538R1 even in standard
  52 // modes before C++26 to avoid breaking the ABI between standard modes (even though ABI
  53 // breaks with std::projected are expected to have essentially no impact).
  54 template <indirectly_readable _It, indirectly_regular_unary_invocable<_It> _Proj>
  55 using projected = typename __projected_impl<_It, _Proj>::__type;
  56
  57 #endif // _LIBCPP_STD_VER >= 20
  58
  59 _LIBCPP_END_NAMESPACE_STD
  60
  61 #endif // _LIBCPP___ITERATOR_PROJECTED_H