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/is_nothrow_constructible.h>
  23 #include <__type_traits/remove_cvref.h>
  24 #include <__utility/forward.h>
  25 #include <__utility/move.h>
  26
  27 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  28 #  pragma GCC system_header
  29 #endif
  30
  31 _LIBCPP_PUSH_MACROS
  32 #include <__undef_macros>
  33
  34 _LIBCPP_BEGIN_NAMESPACE_STD
  35
  36 #if _LIBCPP_STD_VER >= 20
  37
  38 // CRTP base that one can derive from in order to be considered a range adaptor closure
  39 // by the library. When deriving from this class, a pipe operator will be provided to
  40 // make the following hold:
  41 // - `x | f` is equivalent to `f(x)`
  42 // - `f1 | f2` is an adaptor closure `g` such that `g(x)` is equivalent to `f2(f1(x))`
  43 template <class _Tp>
  44 struct __range_adaptor_closure;
  45
  46 // Type that wraps an arbitrary function object and makes it into a range adaptor closure,
  47 // i.e. something that can be called via the `x | f` notation.
  48 template <class _Fn>
  49 struct __range_adaptor_closure_t : _Fn, __range_adaptor_closure<__range_adaptor_closure_t<_Fn>> {
  50     _LIBCPP_HIDE_FROM_ABI constexpr explicit __range_adaptor_closure_t(_Fn&& __f) : _Fn(std::move(__f)) { }
  51 };
  52 _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(__range_adaptor_closure_t);
  53
  54 template <class _Tp>
  55 concept _RangeAdaptorClosure = derived_from<remove_cvref_t<_Tp>, __range_adaptor_closure<remove_cvref_t<_Tp>>>;
  56
  57 template <class _Tp>
  58 struct __range_adaptor_closure {
  59     template <ranges::viewable_range _View, _RangeAdaptorClosure _Closure>
  60         requires same_as<_Tp, remove_cvref_t<_Closure>> &&
  61                  invocable<_Closure, _View>
  62     [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
  63     friend constexpr decltype(auto) operator|(_View&& __view, _Closure&& __closure)
  64         noexcept(is_nothrow_invocable_v<_Closure, _View>)
  65     { return std::invoke(std::forward<_Closure>(__closure), std::forward<_View>(__view)); }
  66
  67     template <_RangeAdaptorClosure _Closure, _RangeAdaptorClosure _OtherClosure>
  68         requires same_as<_Tp, remove_cvref_t<_Closure>> &&
  69                  constructible_from<decay_t<_Closure>, _Closure> &&
  70                  constructible_from<decay_t<_OtherClosure>, _OtherClosure>
  71     [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
  72     friend constexpr auto operator|(_Closure&& __c1, _OtherClosure&& __c2)
  73         noexcept(is_nothrow_constructible_v<decay_t<_Closure>, _Closure> &&
  74                  is_nothrow_constructible_v<decay_t<_OtherClosure>, _OtherClosure>)
  75     { return __range_adaptor_closure_t(std::__compose(std::forward<_OtherClosure>(__c2), std::forward<_Closure>(__c1))); }
  76 };
  77
  78 #endif // _LIBCPP_STD_VER >= 20
  79
  80 _LIBCPP_END_NAMESPACE_STD
  81
  82 _LIBCPP_POP_MACROS
  83
  84 #endif // _LIBCPP___RANGES_RANGE_ADAPTOR_H