[libcxx-commits] [libcxx] [libc++] Implement P2988R12: `std::optional<T&>` (PR #155202)

[A. Jiang via libcxx-commits]

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@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++26
+
+// <optional>
+
+// template <class T> class optional<T&>::iterator;
+// template <class T> class optional<T&>::const_iterator;
+// template <class T>
+// constexpr bool ranges::enable_borrowed_range<optional<T&>> = true;
+
+#include <cassert>
+#include <optional>
+#include <ranges>
+
+template <typename T>
+constexpr void enable_borrowed_range() {
+  static_assert(std::ranges::enable_borrowed_range<std::optional<T&>>);
+}
+
+template <typename T>
+constexpr void borrowed_range() {
+  static_assert(std::ranges::range<std::optional<T&>> == std::ranges::borrowed_range<std::optional<T&>>);
+}
+
+constexpr void test_enable_borrowed_range() {
+  enable_borrowed_range<int>();
+  enable_borrowed_range<const int>();
+  enable_borrowed_range<int[]>();
+  enable_borrowed_range<int[10]>();
+  enable_borrowed_range<int()>();
+}
+
+constexpr void test_borrowed_range() {
+  borrowed_range<int>();
+  borrowed_range<const int>();
+  borrowed_range<int[]>();
+  borrowed_range<int[10]>();
+  borrowed_range<int()>();
+}
+
+int main(int, char**) {
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frederick-vs-ja wrote:

Yeah. That's what I mean by "replace the `main` function with another one".

https://github.com/llvm/llvm-project/pull/155202