[libcxx-commits] [libcxx] [libc++][c++23] P2374: `views::cartesian_product` (PR #111215)

[Hristo Hristov via libcxx-commits]

================
@@ -0,0 +1,69 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// cartesian_product_view() = default;
+
+#include <ranges>
+
+#include <cassert>
+#include <type_traits>
+#include <utility>
+
+constexpr int buff[] = {1, 2, 3};
+
+struct DefaultConstructibleView : std::ranges::view_base {
+  constexpr DefaultConstructibleView() : begin_(buff), end_(buff + 3) {}
+  constexpr int const* begin() const { return begin_; }
+  constexpr int const* end() const { return end_; }
+
+private:
+  int const* begin_;
+  int const* end_;
+};
+
+struct NoDefaultCtrView : std::ranges::view_base {
+  NoDefaultCtrView() = delete;
+  int* begin() const;
+  int* end() const;
+};
+
+// The default constructor requires all underlying views to be default constructible.
+// It is implicitly required by the tuple's constructor. If any of the iterators are
+// not default constructible, cartesian product iterator's =default would be implicitly deleted.
+static_assert(std::is_default_constructible_v<std::ranges::cartesian_product_view<DefaultConstructibleView>>);
+static_assert(std::is_default_constructible_v<
+              std::ranges::cartesian_product_view<DefaultConstructibleView, DefaultConstructibleView>>);
+static_assert(
+    !std::is_default_constructible_v<std::ranges::cartesian_product_view<DefaultConstructibleView, NoDefaultCtrView>>);
+static_assert(
+    !std::is_default_constructible_v<std::ranges::cartesian_product_view<NoDefaultCtrView, NoDefaultCtrView>>);
+static_assert(!std::is_default_constructible_v<std::ranges::cartesian_product_view<NoDefaultCtrView>>);
+
+constexpr bool test() {
+  {
+    using View = std::ranges::cartesian_product_view<DefaultConstructibleView, DefaultConstructibleView>;
+    View v     = View(); // the default constructor is not explicit
+    assert(v.size() == 9);
+    auto it     = v.begin();
+    using Value = std::tuple<const int&, const int&>;
+    assert(*it++ == Value(1, 1));
+    assert(*it++ == Value(1, 2));
+    assert(*it++ == Value(1, 3));
+    assert(*it++ == Value(2, 1));
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+  return 0;
+}
----------------
H-G-Hristov wrote:

```suggestion
}

```

+ empty line at the end of the file.

https://github.com/llvm/llvm-project/pull/111215