libcxx/include/__ranges/range_adaptor.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_RANGE_ADAPTOR_H
  11 #define _LIBCPP___RANGES_RANGE_ADAPTOR_H
  12
  13 #include <__concepts/constructible.h>
  14 #include <__concepts/derived_from.h>
  15 #include <__concepts/invocable.h>
  16 #include <__concepts/same_as.h>
  17 #include <__config>
  18 #include <__functional/compose.h>
  19 #include <__functional/invoke.h>
  20 #include <__ranges/concepts.h>
  21 #include <__type_traits/decay.h>
  22 #include <__type_traits/invoke.h>
  23 #include <__type_traits/is_class.h>
  24 #include <__type_traits/is_nothrow_constructible.h>
  25 #include <__type_traits/remove_cv.h>
  26 #include <__type_traits/remove_cvref.h>
  27 #include <__utility/forward.h>
  28 #include <__utility/move.h>
  29
  30 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  31 #  pragma GCC system_header
  32 #endif
  33
  34 _LIBCPP_PUSH_MACROS
  35 #include <__undef_macros>
  36
  37 _LIBCPP_BEGIN_NAMESPACE_STD
  38
  39 #if _LIBCPP_STD_VER >= 20
  40
  41 namespace ranges {
  42
  43 // CRTP base that one can derive from in order to be considered a range adaptor closure
  44 // by the library. When deriving from this class, a pipe operator will be provided to
  45 // make the following hold:
  46 // - `x | f` is equivalent to `f(x)`
  47 // - `f1 | f2` is an adaptor closure `g` such that `g(x)` is equivalent to `f2(f1(x))`
  48 template <class _Tp>
  49   requires is_class_v<_Tp> && same_as<_Tp, remove_cv_t<_Tp>>
  50 struct __range_adaptor_closure {};
  51
  52 // Type that wraps an arbitrary function object and makes it into a range adaptor closure,
  53 // i.e. something that can be called via the `x | f` notation.
  54 template <class _Fn>
  55 struct __pipeable : _Fn, __range_adaptor_closure<__pipeable<_Fn>> {
  56   _LIBCPP_HIDE_FROM_ABI constexpr explicit __pipeable(_Fn&& __f) : _Fn(std::move(__f)) {}
  57 };
  58 _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(__pipeable);
  59
  60 template <class _Tp>
  61 _Tp __derived_from_range_adaptor_closure(__range_adaptor_closure<_Tp>*);
  62
  63 template <class _Tp>
  64 concept _RangeAdaptorClosure = !ranges::range<remove_cvref_t<_Tp>> && requires {
  65   // Ensure that `remove_cvref_t<_Tp>` is derived from `__range_adaptor_closure<remove_cvref_t<_Tp>>` and isn't derived
  66   // from `__range_adaptor_closure<U>` for any other type `U`.
  67   { ranges::__derived_from_range_adaptor_closure((remove_cvref_t<_Tp>*)nullptr) } -> same_as<remove_cvref_t<_Tp>>;
  68 };
  69
  70 template <ranges::range _Range, _RangeAdaptorClosure _Closure>
  71   requires invocable<_Closure, _Range>
  72 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto)
  73 operator|(_Range&& __range, _Closure&& __closure) noexcept(is_nothrow_invocable_v<_Closure, _Range>) {
  74   return std::invoke(std::forward<_Closure>(__closure), std::forward<_Range>(__range));
  75 }
  76
  77 template <_RangeAdaptorClosure _Closure, _RangeAdaptorClosure _OtherClosure>
  78   requires constructible_from<decay_t<_Closure>, _Closure> && constructible_from<decay_t<_OtherClosure>, _OtherClosure>
  79 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator|(_Closure&& __c1, _OtherClosure&& __c2) noexcept(
  80     is_nothrow_constructible_v<decay_t<_Closure>, _Closure> &&
  81     is_nothrow_constructible_v<decay_t<_OtherClosure>, _OtherClosure>) {
  82   return __pipeable(std::__compose(std::forward<_OtherClosure>(__c2), std::forward<_Closure>(__c1)));
  83 }
  84
  85 #  if _LIBCPP_STD_VER >= 23
  86 template <class _Tp>
  87   requires is_class_v<_Tp> && same_as<_Tp, remove_cv_t<_Tp>>
  88 class range_adaptor_closure : public __range_adaptor_closure<_Tp> {};
  89 #  endif // _LIBCPP_STD_VER >= 23
  90
  91 } // namespace ranges
  92
  93 #endif // _LIBCPP_STD_VER >= 20
  94
  95 _LIBCPP_END_NAMESPACE_STD
  96
  97 _LIBCPP_POP_MACROS
  98
  99 #endif // _LIBCPP___RANGES_RANGE_ADAPTOR_H