[libcxx-commits] [libcxx] [libc++][ranges] P2164R9: Implements `views::enumerate` (PR #73617)

[Louis Dionne via libcxx-commits]

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@@ -0,0 +1,108 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++23
+
+// <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;
+
+    compareOperatorTest(it1, it2);
+
+    assert((it1 <=> it2) == std::strong_ordering::less);
+    assert((it1 <=> it1) == std::strong_ordering::equal);
+    assert((it2 <=> it2) == std::strong_ordering::equal);
+    assert((it2 <=> it1) == std::strong_ordering::greater);
+  }
+
+  // Test an old-school iterator with no operator<=>
+  {
+    using Iterator = random_access_iterator<int*>;
+    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>>);
+
+    auto ev  = Subrange{Iterator{buff}, Iterator{buff + 3}} | std::views::enumerate;
+    auto it1 = ev.begin();
+    auto it2 = it1 + 1;
----------------
ldionne wrote:

>From Chris: same here, please const-qualify.

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