[libcxx][ranges] Add class ref_view.

Differential Revision: https://reviews.llvm.org/D102020

libcxx/include/CMakeLists.txt

@@ -51,6 +51,7 @@ set(files
   __ranges/enable_borrowed_range.h
   __ranges/enable_view.h
   __ranges/view_interface.h
+  __ranges/ref_view.h
   __ranges/size.h
   __ranges/subrange.h
   __split_buffer

libcxx/include/__ranges/ref_view.h

@@ -0,0 +1,78 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+#ifndef _LIBCPP___RANGES_REF_VIEW_H
+#define _LIBCPP___RANGES_REF_VIEW_H
+
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__ranges/access.h>
+#include <__ranges/data.h>
+#include <__ranges/view_interface.h>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if !defined(_LIBCPP_HAS_NO_RANGES)
+
+namespace ranges {
+  template<range _Range>
+    requires is_object_v<_Range>
+  class ref_view : public view_interface<ref_view<_Range>> {
+    _Range *__range_;
+
+    static void __fun(_Range&);
+    static void __fun(_Range&&) = delete;
+
+public:
+    template<class _Tp>
+      requires __different_from<_Tp, ref_view> &&
+        convertible_to<_Tp, _Range&> && requires { __fun(declval<_Tp>()); }
+    constexpr ref_view(_Tp&& __t)
+      : __range_(_VSTD::addressof(static_cast<_Range&>(_VSTD::forward<_Tp>(__t))))
+    {}
+
+    constexpr _Range& base() const { return *__range_; }
+
+    constexpr iterator_t<_Range> begin() const { return ranges::begin(*__range_); }
+    constexpr sentinel_t<_Range> end() const { return ranges::end(*__range_); }
+
+    constexpr bool empty() const
+      requires requires { ranges::empty(*__range_); }
+    { return ranges::empty(*__range_); }
+
+    constexpr auto size() const
+      requires sized_range<_Range>
+    { return ranges::size(*__range_); }
+
+    // TODO: This needs to use contiguous_range.
+    constexpr auto data() const
+      requires contiguous_iterator<iterator_t<_Range>>
+    { return ranges::data(*__range_); }
+  };
+
+  template<class _Range>
+  ref_view(_Range&) -> ref_view<_Range>;
+
+} // namespace ranges
+
+#endif // !defined(_LIBCPP_HAS_NO_RANGES)
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___RANGES_REF_VIEW_H

libcxx/include/ranges

@@ -100,6 +100,7 @@ namespace std::ranges {
 #include <__ranges/empty_view.h>
 #include <__ranges/enable_borrowed_range.h>
 #include <__ranges/enable_view.h>
+#include <__ranges/ref_view.h>
 #include <__ranges/size.h>
 #include <__ranges/subrange.h>
 #include <__ranges/view_interface.h>

libcxx/test/std/ranges/range.adaptors/range.ref.view.pass.cpp

@@ -0,0 +1,208 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// std::ranges::ref_view
+
+#include <ranges>
+
+#include <cassert>
+#include "test_macros.h"
+#include "test_iterators.h"
+
+int globalBuff[8];
+
+template<class T>
+concept ValidRefView = requires { typename std::ranges::ref_view<T>; };
+
+struct Range {
+  int start = 0;
+  friend constexpr int* begin(Range const& range) { return globalBuff + range.start; }
+  friend constexpr int* end(Range const&) { return globalBuff + 8; }
+  friend constexpr int* begin(Range& range) { return globalBuff + range.start; }
+  friend constexpr int* end(Range&) { return globalBuff + 8; }
+};
+
+struct BeginOnly {
+  friend int* begin(BeginOnly const&);
+  friend int* begin(BeginOnly &);
+};
+
+static_assert( ValidRefView<Range>);
+static_assert(!ValidRefView<BeginOnly>);
+static_assert(!ValidRefView<int (&)[4]>);
+static_assert( ValidRefView<int[4]>);
+
+static_assert(std::derived_from<std::ranges::ref_view<Range>, std::ranges::view_interface<std::ranges::ref_view<Range>>>);
+
+struct RangeConvertible {
+  operator Range& ();
+};
+
+struct RValueRangeConvertible {
+  operator Range&& ();
+};
+
+static_assert( std::is_constructible_v<std::ranges::ref_view<Range>, Range&>);
+static_assert( std::is_constructible_v<std::ranges::ref_view<Range>, RangeConvertible>);
+static_assert(!std::is_constructible_v<std::ranges::ref_view<Range>, RValueRangeConvertible>);
+
+struct ConstConvertibleToLValueAndRValue {
+  operator Range& () const;
+  operator Range&& () const;
+};
+static_assert( std::is_convertible_v<RangeConvertible, std::ranges::ref_view<Range>>);
+static_assert(!std::is_convertible_v<RValueRangeConvertible, std::ranges::ref_view<Range>>);
+static_assert(!std::is_convertible_v<ConstConvertibleToLValueAndRValue, std::ranges::ref_view<Range>>);
+
+struct ForwardRange {
+  constexpr forward_iterator<int*> begin() const { return forward_iterator<int*>(globalBuff); }
+  constexpr forward_iterator<int*> end() const { return forward_iterator<int*>(globalBuff + 8); }
+};
+
+struct Cpp17InputRange {
+  struct sentinel {
+    friend constexpr bool operator==(sentinel, cpp17_input_iterator<int*> iter) { return iter.base() == globalBuff + 8; }
+    friend constexpr std::ptrdiff_t operator-(sentinel, cpp17_input_iterator<int*>) { return -8; }
+    friend constexpr std::ptrdiff_t operator-(cpp17_input_iterator<int*>, sentinel) { return 8; }
+  };
+
+  constexpr cpp17_input_iterator<int*> begin() const {
+    return cpp17_input_iterator<int*>(globalBuff);
+  }
+  constexpr sentinel end() const { return {}; }
+};
+
+struct Cpp20InputRange {
+  struct sentinel {
+    friend constexpr bool operator==(sentinel, const cpp20_input_iterator<int*> &iter) { return iter.base() == globalBuff + 8; }
+    friend constexpr std::ptrdiff_t operator-(sentinel, const cpp20_input_iterator<int*>&) { return -8; }
+  };
+
+  constexpr cpp20_input_iterator<int*> begin() const {
+    return cpp20_input_iterator<int*>(globalBuff);
+  }
+  constexpr sentinel end() const { return {}; }
+};
+
+template<>
+inline constexpr bool std::ranges::enable_borrowed_range<Cpp20InputRange> = true;
+
+template<class R>
+concept EmptyIsInvocable = requires (std::ranges::ref_view<R> view) { view.empty(); };
+
+template<class R>
+concept SizeIsInvocable = requires (std::ranges::ref_view<R> view) { view.size(); };
+
+template<class R>
+concept DataIsInvocable = requires (std::ranges::ref_view<R> view) { view.data(); };
+
+// Testing ctad.
+static_assert(std::same_as<decltype(std::ranges::ref_view(std::declval<Range&>())),
+              std::ranges::ref_view<Range>>);
+
+constexpr bool test() {
+  {
+    // ref_view::base
+    Range range;
+    std::ranges::ref_view<Range> view{range};
+    assert(view.begin() == globalBuff);
+    view.base() = Range{2};
+    assert(view.begin() == globalBuff + 2);
+  }
+
+  {
+    // ref_view::begin
+    Range range1;
+    std::ranges::ref_view<Range> view1 = range1;
+    assert(view1.begin() == globalBuff);
+
+    ForwardRange range2;
+    std::ranges::ref_view<ForwardRange> view2 = range2;
+    assert(view2.begin().base() == globalBuff);
+
+    Cpp17InputRange range3;
+    std::ranges::ref_view<Cpp17InputRange> view3 = range3;
+    assert(view3.begin().base() == globalBuff);
+
+    Cpp20InputRange range4;
+    std::ranges::ref_view<Cpp20InputRange> view4 = range4;
+    assert(view4.begin().base() == globalBuff);
+  }
+
+  {
+    // ref_view::end
+    Range range1;
+    std::ranges::ref_view<Range> view1 = range1;
+    assert(view1.end() == globalBuff + 8);
+
+    ForwardRange range2;
+    std::ranges::ref_view<ForwardRange> view2 = range2;
+    assert(view2.end().base() == globalBuff + 8);
+
+    Cpp17InputRange range3;
+    std::ranges::ref_view<Cpp17InputRange> view3 = range3;
+    assert(view3.end() == cpp17_input_iterator(globalBuff + 8));
+
+    Cpp20InputRange range4;
+    std::ranges::ref_view<Cpp20InputRange> view4 = range4;
+    assert(view4.end() == cpp20_input_iterator(globalBuff + 8));
+  }
+
+  {
+    // ref_view::empty
+    Range range{8};
+    std::ranges::ref_view<Range> view1 = range;
+    assert(view1.empty());
+
+    ForwardRange range2;
+    std::ranges::ref_view<ForwardRange> view2 = range2;
+    assert(!view2.empty());
+
+    static_assert(!EmptyIsInvocable<Cpp17InputRange>);
+    static_assert(!EmptyIsInvocable<Cpp20InputRange>);
+  }
+
+  {
+    // ref_view::size
+    Range range1{8};
+    std::ranges::ref_view<Range> view1 = range1;
+    assert(view1.size() == 0);
+
+    Range range2{2};
+    std::ranges::ref_view<Range> view2 = range2;
+    assert(view2.size() == 6);
+
+    static_assert(!SizeIsInvocable<ForwardRange>);
+  }
+
+  {
+    // ref_view::data
+    Range range1;
+    std::ranges::ref_view<Range> view1 = range1;
+    assert(view1.data() == globalBuff);
+
+    Range range2{2};
+    std::ranges::ref_view<Range> view2 = range2;
+    assert(view2.data() == globalBuff + 2);
+
+    static_assert(!DataIsInvocable<ForwardRange>);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}