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

[Christopher Di Bella via libcxx-commits]

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@@ -0,0 +1,77 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// constexpr auto operator[](difference_type n) const
+//   requires random_access_range<Base>;
+
+#include <array>
+#include <cassert>
+#include <ranges>
+#include <tuple>
+
+#include "test_iterators.h"
+
+template <class T, class U>
+concept HasSubscriptOperator = requires(T t, U u) { t[u]; };
+
+template <class BaseRange>
+using EnumerateIterator = std::ranges::iterator_t<std::ranges::enumerate_view<BaseRange>>;
+
+using RandomAccessRange = std::ranges::subrange<int*>;
+static_assert(std::ranges::random_access_range<RandomAccessRange>);
+
+static_assert(HasSubscriptOperator<EnumerateIterator<RandomAccessRange>, int>);
+
+using BidirectionalRange = std::ranges::subrange<bidirectional_iterator<int*>>;
+static_assert(!std::ranges::random_access_range<BidirectionalRange>);
+
+static_assert(!HasSubscriptOperator<EnumerateIterator<BidirectionalRange>, int>);
+
+constexpr bool test() {
+  // Reference
+  {
+    std::array ts = {0, 1, 2, 3, 84};
+    auto view     = ts | std::views::enumerate;
+    auto it       = view.begin();
+
+    for (std::size_t index = 0; index != ts.size(); ++index) {
+      assert(it[index] == *(it + index));
+    }
+
+    static_assert(std::is_same_v<decltype(it[2]), std::tuple<decltype(it)::difference_type, int&>>);
+  }
+
+  // Value
+  {
+    auto view = std::views::iota(0, 5) | std::views::enumerate;
+    auto it   = view.begin();
+
+    for (std::size_t index = 0; index != 5; ++index) {
+      assert(it[index] == *(it + index));
+    }
+
+    static_assert(std::is_same_v<decltype(it[2]), std::tuple<decltype(it)::difference_type, int>>);
----------------
cjdb wrote:

Consider using `std::iter_difference_t`.

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