[libcxx] [llvm] [lld] [flang] [clang-tools-extra] [clang] [compiler-rt] [libc++][ranges] P2116R9: Implements `views::enumerate` (PR #73617)

[Christopher Di Bella via cfe-commits]

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@@ -0,0 +1,107 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// <ranges>
+
+// class enumerate_view
+
+// class enumerate_view::iterator
+
+// friend constexpr strong_ordering operator<=>(const iterator& x, const iterator& y) noexcept;
+
+#include <cassert>
+#include <ranges>
+
+#include "test_iterators.h"
+#include "../types.h"
+
+constexpr void compareOperatorTest(const auto& iter1, const auto& iter2) {
+  assert(!(iter1 < iter1));
+  assert(iter1 < iter2);
+  assert(!(iter2 < iter1));
+
+  assert(iter1 <= iter1);
+  assert(iter1 <= iter2);
+  assert(!(iter2 <= iter1));
+
+  assert(!(iter1 > iter1));
+  assert(!(iter1 > iter2));
+  assert(iter2 > iter1);
+
+  assert(iter1 >= iter1);
+  assert(!(iter1 >= iter2));
+  assert(iter2 >= iter1);
+
+  assert(iter1 == iter1);
+  assert(!(iter1 == iter2));
+  assert(iter2 == iter2);
+
+  assert(!(iter1 != iter1));
+  assert(iter1 != iter2);
+  assert(!(iter2 != iter2));
+}
+
+constexpr bool test() {
+  int buff[] = {0, 1, 2, 3};
+  {
+    using View = std::ranges::enumerate_view<RangeView>;
+
+    using Iterator = std::ranges::iterator_t<View>;
+    static_assert(std::three_way_comparable<Iterator>);
+    using Subrange = std::ranges::subrange<Iterator>;
+    static_assert(std::three_way_comparable<std::ranges::iterator_t<Subrange>>);
+    using EnumerateView = std::ranges::enumerate_view<Subrange>;
+    static_assert(std::three_way_comparable<std::ranges::iterator_t<EnumerateView>>);
+
+    RangeView const range(buff, buff + 4);
+
+    std::same_as<View> decltype(auto) ev = std::views::enumerate(range);
+
+    auto it1 = ev.begin();
+    auto it2 = it1 + 1;
----------------
cjdb wrote:

Please const-qualify (I'm specifically calling these out because the interface requires them to be `const`-qualified).

https://github.com/llvm/llvm-project/pull/73617