[libc++] Add range_size_t

Differential Revision: https://reviews.llvm.org/D106708

libcxx/docs/Status/RangesPaper.csv

@@ -103,10 +103,10 @@ Section,Description,Dependencies,Assignee,Complete
 | `ranges::iterator_t <https://llvm.org/D100255>`_
 | `ranges::sentinel_t <https://llvm.org/D100269>`_
 | `ranges::range_difference_t <https://llvm.org/D100269>`_
-| ranges::range_size_t
+| `ranges::range_size_t <https://llvm.org/D106708>`_
 | `ranges::range_value_t <https://llvm.org/D100269>`_
 | `ranges::range_reference_t <https://llvm.org/D100269>`_
-| `ranges::range_rvalue_reference_t <https://llvm.org/D100269>`_",[range.access],Christopher Di Bella,In progress
+| `ranges::range_rvalue_reference_t <https://llvm.org/D100269>`_",[range.access],Christopher Di Bella,✅
 `[range.sized] <http://wg21.link/range.sized>`_,"| `ranges::sized_range <https://llvm.org/D102434>`_
 | `ranges::disable_sized_range <https://llvm.org/D102434>`_","| [range.primitives]
 | [range.range]",Christopher Di Bella,✅

libcxx/include/__ranges/concepts.h

@@ -69,6 +69,9 @@ namespace ranges {
   template <class _Tp>
   concept sized_range = range<_Tp> && requires(_Tp& __t) { ranges::size(__t); };
 
+  template<sized_range _Rp>
+  using range_size_t = decltype(ranges::size(declval<_Rp&>()));
+
   // `disable_sized_range` defined in `<__ranges/size.h>`
 
   // [range.view], views

libcxx/include/ranges

@@ -36,13 +36,13 @@ namespace std::ranges {
     inline constexpr bool enable_borrowed_range = false;
 
   template<class T>
-    using iterator_t = decltype(ranges::begin(declval<T&>()));
-  template<class T>
-    using iterator_t = decltype(ranges::begin(declval<T&>()));
+    using iterator_t = decltype(ranges::begin(declval<R&>()));
   template<range R>
     using sentinel_t = decltype(ranges::end(declval<R&>()));
   template<range R>
     using range_difference_t = iter_difference_t<iterator_t<R>>;
+  template<sized_range R>
+    using range_size_t = decltype(ranges::size(declval<R&>()));
   template<range R>
     using range_value_t = iter_value_t<iterator_t<R>>;
   template<range R>

libcxx/test/std/ranges/range.req/range.range/range_size_t.compile.pass.cpp

@@ -0,0 +1,42 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// template<sized_range R>
+// using range_size_t = decltype(ranges::size(declval<R&>()));
+
+#include <ranges>
+#include <concepts>
+#include <cstddef>
+
+#include "test_iterators.h"
+
+template<class T>
+concept has_range_size_t = requires { typename std::ranges::range_size_t<T>; };
+
+struct A { int *begin(); int *end(); short size(); };
+static_assert(std::same_as<std::ranges::range_size_t<A>, short>);
+static_assert(std::same_as<std::ranges::range_size_t<A&>, short>);
+static_assert(std::same_as<std::ranges::range_size_t<A&&>, short>);
+static_assert(!has_range_size_t<const A>);
+static_assert(!has_range_size_t<const A&>);
+static_assert(!has_range_size_t<const A&&>);
+
+struct B { int *begin(); int *end(); };
+static_assert(std::same_as<std::ranges::range_size_t<B>, std::size_t>);
+static_assert(std::same_as<std::ranges::range_size_t<B&>, std::size_t>);
+static_assert(std::same_as<std::ranges::range_size_t<B&&>, std::size_t>);
+static_assert(!has_range_size_t<const B>);
+static_assert(!has_range_size_t<const B&>);
+static_assert(!has_range_size_t<const B&&>);
+
+struct C { bidirectional_iterator<int*> begin(); bidirectional_iterator<int*> end(); };
+static_assert(!has_range_size_t<C>);