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[libc++][ranges] P2387R3: Pipe support for user-defined range adaptors (
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#89148)

This patch finalizes the std::ranges::range_adaptor_closure
class template from https://wg21.link/P2387R3.

  // [range.adaptor.object], range adaptor objects
  template<class D>
    requires is_class_v<D> && same_as<D, remove_cv_t<D>>
  class range_adaptor_closure { };

The current implementation of __range_adaptor_closure was introduced
in ee44dd8 and has served as the
foundation for the range adaptors in libc++ for a while. This patch
keeps its implementation, with the exception of the following changes:

- __range_adaptor_closure now includes the missing constraints
  `is_class_v<D> && same_as<D, remove_cv_t<D>>` to restrict the 
  type of class that can inherit from it. (https://eel.is/c++draft/ranges.syn)
- The operator| of __range_adaptor_closure no longer requires its
  first argument to model viewable_range. (https://eel.is/c++draft/range.adaptor.object#1)
- The _RangeAdaptorClosure concept is refined to exclude cases where
  T models range or where T has base classes of type range_adaptor_closure<U>
  for another type U. (https://eel.is/c++draft/range.adaptor.object#2)
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xiaoyang-sde committed Apr 23, 2024
1 parent adb0126 commit c108653
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1 change: 1 addition & 0 deletions libcxx/docs/ReleaseNotes/19.rst
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Expand Up @@ -49,6 +49,7 @@ Implemented Papers
- P2302R4 - ``std::ranges::contains``
- P1659R3 - ``std::ranges::starts_with`` and ``std::ranges::ends_with``
- P3029R1 - Better ``mdspan``'s CTAD
- P2387R3 - Pipe support for user-defined range adaptors

Improvements and New Features
-----------------------------
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1 change: 0 additions & 1 deletion libcxx/docs/Status/Cxx23.rst
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Expand Up @@ -43,7 +43,6 @@ Paper Status
.. [#note-P0533R9] P0533R9: ``isfinite``, ``isinf``, ``isnan`` and ``isnormal`` are implemented.
.. [#note-P1413R3] P1413R3: ``std::aligned_storage_t`` and ``std::aligned_union_t`` are marked deprecated, but
clang doesn't issue a diagnostic for deprecated using template declarations.
.. [#note-P2387R3] P2387R3: ``bind_back`` only
.. [#note-P2520R0] P2520R0: Libc++ implemented this paper as a DR in C++20 as well.
.. [#note-P2711R1] P2711R1: ``join_with_view`` hasn't been done yet since this type isn't implemented yet.
.. [#note-P2770R0] P2770R0: ``join_with_view`` hasn't been done yet since this type isn't implemented yet.
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2 changes: 1 addition & 1 deletion libcxx/docs/Status/Cxx23Papers.csv
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Expand Up @@ -45,7 +45,7 @@
"`P1413R3 <https://wg21.link/P1413R3>`__","LWG","Deprecate ``std::aligned_storage`` and ``std::aligned_union``","February 2022","|Complete| [#note-P1413R3]_",""
"`P2255R2 <https://wg21.link/P2255R2>`__","LWG","A type trait to detect reference binding to temporary","February 2022","",""
"`P2273R3 <https://wg21.link/P2273R3>`__","LWG","Making ``std::unique_ptr`` constexpr","February 2022","|Complete|","16.0"
"`P2387R3 <https://wg21.link/P2387R3>`__","LWG","Pipe support for user-defined range adaptors","February 2022","|Partial| [#note-P2387R3]_","","|ranges|"
"`P2387R3 <https://wg21.link/P2387R3>`__","LWG","Pipe support for user-defined range adaptors","February 2022","|Complete|","19.0","|ranges|"
"`P2440R1 <https://wg21.link/P2440R1>`__","LWG","``ranges::iota``, ``ranges::shift_left`` and ``ranges::shift_right``","February 2022","","","|ranges|"
"`P2441R2 <https://wg21.link/P2441R2>`__","LWG","``views::join_with``","February 2022","|In Progress|","","|ranges|"
"`P2442R1 <https://wg21.link/P2442R1>`__","LWG","Windowing range adaptors: ``views::chunk`` and ``views::slide``","February 2022","","","|ranges|"
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2 changes: 1 addition & 1 deletion libcxx/docs/Status/RangesMajorFeatures.csv
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@@ -1,5 +1,5 @@
Standard,Name,Assignee,CL,Status
C++23,`ranges::to <https://wg21.link/P1206R7>`_,Konstantin Varlamov,`D142335 <https://reviews.llvm.org/D142335>`_,Complete
C++23,`Pipe support for user-defined range adaptors <https://wg21.link/P2387R3>`_,Unassigned,No patch yet,Not started
C++23,`Pipe support for user-defined range adaptors <https://wg21.link/P2387R3>`_,"Louis Dionne, Jakub Mazurkiewicz, and Xiaoyang Liu",Various,Complete
C++23,`Formatting Ranges <https://wg21.link/P2286R8>`_,Mark de Wever,Various,Complete
C++20,`Stashing stashing iterators for proper flattening <https://wg21.link/P2770R0>`_,Jakub Mazurkiewicz,Various,In progress
53 changes: 36 additions & 17 deletions libcxx/include/__ranges/range_adaptor.h
Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
#include <__functional/invoke.h>
#include <__ranges/concepts.h>
#include <__type_traits/decay.h>
#include <__type_traits/is_class.h>
#include <__type_traits/is_nothrow_constructible.h>
#include <__type_traits/remove_cvref.h>
#include <__utility/forward.h>
Expand All @@ -35,12 +36,15 @@ _LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER >= 20

namespace ranges {

// CRTP base that one can derive from in order to be considered a range adaptor closure
// by the library. When deriving from this class, a pipe operator will be provided to
// make the following hold:
// - `x | f` is equivalent to `f(x)`
// - `f1 | f2` is an adaptor closure `g` such that `g(x)` is equivalent to `f2(f1(x))`
template <class _Tp>
requires is_class_v<_Tp> && same_as<_Tp, remove_cv_t<_Tp>>
struct __range_adaptor_closure;

// Type that wraps an arbitrary function object and makes it into a range adaptor closure,
Expand All @@ -52,27 +56,42 @@ struct __range_adaptor_closure_t : _Fn, __range_adaptor_closure<__range_adaptor_
_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(__range_adaptor_closure_t);

template <class _Tp>
concept _RangeAdaptorClosure = derived_from<remove_cvref_t<_Tp>, __range_adaptor_closure<remove_cvref_t<_Tp>>>;
_Tp __derived_from_range_adaptor_closure(__range_adaptor_closure<_Tp>*);

template <class _Tp>
struct __range_adaptor_closure {
template <ranges::viewable_range _View, _RangeAdaptorClosure _Closure>
requires same_as<_Tp, remove_cvref_t<_Closure>> && invocable<_Closure, _View>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr decltype(auto)
operator|(_View&& __view, _Closure&& __closure) noexcept(is_nothrow_invocable_v<_Closure, _View>) {
return std::invoke(std::forward<_Closure>(__closure), std::forward<_View>(__view));
}

template <_RangeAdaptorClosure _Closure, _RangeAdaptorClosure _OtherClosure>
requires same_as<_Tp, remove_cvref_t<_Closure>> && constructible_from<decay_t<_Closure>, _Closure> &&
constructible_from<decay_t<_OtherClosure>, _OtherClosure>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr auto operator|(_Closure&& __c1, _OtherClosure&& __c2) noexcept(
is_nothrow_constructible_v<decay_t<_Closure>, _Closure> &&
is_nothrow_constructible_v<decay_t<_OtherClosure>, _OtherClosure>) {
return __range_adaptor_closure_t(std::__compose(std::forward<_OtherClosure>(__c2), std::forward<_Closure>(__c1)));
}
concept _RangeAdaptorClosure = !ranges::range<remove_cvref_t<_Tp>> && requires {
// Ensure that `remove_cvref_t<_Tp>` is derived from `__range_adaptor_closure<remove_cvref_t<_Tp>>` and isn't derived
// from `__range_adaptor_closure<U>` for any other type `U`.
{ ranges::__derived_from_range_adaptor_closure((remove_cvref_t<_Tp>*)nullptr) } -> same_as<remove_cvref_t<_Tp>>;
};

template <ranges::range _Range, _RangeAdaptorClosure _Closure>
requires invocable<_Closure, _Range>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto)
operator|(_Range&& __range, _Closure&& __closure) noexcept(is_nothrow_invocable_v<_Closure, _Range>) {
return std::invoke(std::forward<_Closure>(__closure), std::forward<_Range>(__range));
}

template <_RangeAdaptorClosure _Closure, _RangeAdaptorClosure _OtherClosure>
requires constructible_from<decay_t<_Closure>, _Closure> && constructible_from<decay_t<_OtherClosure>, _OtherClosure>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator|(_Closure&& __c1, _OtherClosure&& __c2) noexcept(
is_nothrow_constructible_v<decay_t<_Closure>, _Closure> &&
is_nothrow_constructible_v<decay_t<_OtherClosure>, _OtherClosure>) {
return __range_adaptor_closure_t(std::__compose(std::forward<_OtherClosure>(__c2), std::forward<_Closure>(__c1)));
}

template <class _Tp>
requires is_class_v<_Tp> && same_as<_Tp, remove_cv_t<_Tp>>
struct __range_adaptor_closure {};

# if _LIBCPP_STD_VER >= 23
template <class _Tp>
requires is_class_v<_Tp> && same_as<_Tp, remove_cv_t<_Tp>>
class range_adaptor_closure : public __range_adaptor_closure<_Tp> {};
# endif // _LIBCPP_STD_VER >= 23

} // namespace ranges

#endif // _LIBCPP_STD_VER >= 20

_LIBCPP_END_NAMESPACE_STD
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5 changes: 5 additions & 0 deletions libcxx/include/ranges
Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,11 @@ namespace std::ranges {
template<class T>
concept viewable_range = see below;
// [range.adaptor.object], range adaptor objects
template<class D>
requires is_class_v<D> && same_as<D, remove_cv_t<D>>
class range_adaptor_closure { }; // Since c++23
// [view.interface], class template view_interface
template<class D>
requires is_class_v<D> && same_as<D, remove_cv_t<D>>
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Original file line number Diff line number Diff line change
@@ -0,0 +1,142 @@
//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20

// std::ranges::range_adaptor_closure;

#include <ranges>

#include <algorithm>
#include <vector>

#include "test_range.h"

template <class T>
concept CanDeriveFromRangeAdaptorClosure = requires { typename std::ranges::range_adaptor_closure<T>; };
static_assert(!CanDeriveFromRangeAdaptorClosure<int>);

struct Foo {};
static_assert(CanDeriveFromRangeAdaptorClosure<Foo>);
static_assert(!CanDeriveFromRangeAdaptorClosure<Foo&>);
static_assert(!CanDeriveFromRangeAdaptorClosure<const Foo>);
static_assert(!CanDeriveFromRangeAdaptorClosure<volatile Foo>);
static_assert(!CanDeriveFromRangeAdaptorClosure<const volatile Foo&&>);

struct incomplete_t;
static_assert(CanDeriveFromRangeAdaptorClosure<incomplete_t>);

using range_t = std::vector<int>;

template <class T>
concept RangeAdaptorClosure =
CanBePiped<range_t, T&> && CanBePiped<range_t, const T&> && CanBePiped<range_t, T&&> &&
CanBePiped<range_t, const T&&>;

struct callable : std::ranges::range_adaptor_closure<callable> {
static void operator()(const range_t&) {}
};
static_assert(RangeAdaptorClosure<callable>);

// `not_callable_1` doesn't have an `operator()`
struct not_callable_1 : std::ranges::range_adaptor_closure<not_callable_1> {};
static_assert(!RangeAdaptorClosure<not_callable_1>);

// `not_callable_2` doesn't have an `operator()` that accepts a `range` argument
struct not_callable_2 : std::ranges::range_adaptor_closure<not_callable_2> {
static void operator()() {}
};
static_assert(!RangeAdaptorClosure<not_callable_2>);

// `not_derived_from_1` doesn't derive from `std::ranges::range_adaptor_closure`
struct not_derived_from_1 {
static void operator()(const range_t&) {}
};
static_assert(!RangeAdaptorClosure<not_derived_from_1>);

// `not_derived_from_2` doesn't publicly derive from `std::ranges::range_adaptor_closure`
struct not_derived_from_2 : private std::ranges::range_adaptor_closure<not_derived_from_2> {
static void operator()(const range_t&) {}
};
static_assert(!RangeAdaptorClosure<not_derived_from_2>);

// `not_derived_from_3` doesn't derive from the correct specialization of `std::ranges::range_adaptor_closure`
struct not_derived_from_3 : std::ranges::range_adaptor_closure<callable> {
static void operator()(const range_t&) {}
};
static_assert(!RangeAdaptorClosure<not_derived_from_3>);

// `not_derived_from_4` doesn't derive from exactly one specialization of `std::ranges::range_adaptor_closure`
struct not_derived_from_4
: std::ranges::range_adaptor_closure<not_derived_from_4>,
std::ranges::range_adaptor_closure<callable> {
static void operator()(const range_t&) {}
};
static_assert(!RangeAdaptorClosure<not_derived_from_4>);

// `is_range` models `range`
struct is_range : std::ranges::range_adaptor_closure<is_range> {
static void operator()(const range_t&) {}
int* begin() const { return nullptr; }
int* end() const { return nullptr; }
};
static_assert(std::ranges::range<is_range> && std::ranges::range<const is_range>);
static_assert(!RangeAdaptorClosure<is_range>);

// user-defined range adaptor closure object
struct negate_fn : std::ranges::range_adaptor_closure<negate_fn> {
template <std::ranges::range Range>
static constexpr decltype(auto) operator()(Range&& range) {
return std::forward<Range>(range) | std::views::transform([](auto element) { return -element; });
}
};
static_assert(RangeAdaptorClosure<negate_fn>);
constexpr auto negate = negate_fn{};

// user-defined range adaptor closure object
struct plus_1_fn : std::ranges::range_adaptor_closure<plus_1_fn> {
template <std::ranges::range Range>
static constexpr decltype(auto) operator()(Range&& range) {
return std::forward<Range>(range) | std::views::transform([](auto element) { return element + 1; });
}
};
static_assert(RangeAdaptorClosure<plus_1_fn>);
constexpr auto plus_1 = plus_1_fn{};

constexpr bool test() {
const std::vector<int> n{1, 2, 3, 4, 5};
const std::vector<int> n_negate{-1, -2, -3, -4, -5};

assert(std::ranges::equal(n | negate, n_negate));
assert(std::ranges::equal(negate(n), n_negate));

assert(std::ranges::equal(n | negate | negate, n));
assert(std::ranges::equal(n | (negate | negate), n));
assert(std::ranges::equal((n | negate) | negate, n));
assert(std::ranges::equal(negate(n) | negate, n));
assert(std::ranges::equal(negate(n | negate), n));
assert(std::ranges::equal((negate | negate)(n), n));
assert(std::ranges::equal(negate(negate(n)), n));

const std::vector<int> n_plus_1_negate{-2, -3, -4, -5, -6};
assert(std::ranges::equal(n | plus_1 | negate, n_plus_1_negate));
assert(std::ranges::equal(
n | plus_1 | std::views::transform([](auto element) { return element; }) | negate, n_plus_1_negate));

const std::vector<int> n_negate_plus_1{0, -1, -2, -3, -4};
assert(std::ranges::equal(n | negate | plus_1, n_negate_plus_1));
assert(std::ranges::equal(n | std::views::reverse | negate | plus_1 | std::views::reverse, n_negate_plus_1));
return true;
}

int main(int, char**) {
test();
static_assert(test());

return 0;
}

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