views::cartesian_product + test

Author: PaulXiCao

libcxx/include/__ranges/cartesian_product_view.h

@@ -450,6 +450,22 @@ class cartesian_product_view<First, Vs...>::iterator {
   }
 };
 
+namespace views {
+namespace __cartesian_product {
+struct __fn {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI static constexpr auto operator()() { return views::single(tuple()); }
+
+  template <class... _Ranges>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI static constexpr auto operator()(_Ranges&&... __rs)
+      -> decltype(cartesian_product_view<all_t<_Ranges&&>...>(std::forward<_Ranges>(__rs)...)) {
+    return cartesian_product_view<all_t<_Ranges>...>(std::forward<_Ranges>(__rs)...);
+  }
+};
+} // namespace __cartesian_product
+inline namespace __cpo {
+inline constexpr auto cartesian_product = __cartesian_product::__fn{};
+} // namespace __cpo
+} // namespace views
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/test/std/ranges/range.adaptors/range.cartesian.product.view/example_from_std.pass.cpp

@@ -28,8 +28,7 @@ constexpr bool test() {
 
   const std::vector<int> v{0, 1, 2};
   ConstexprStringStream out;
-  // fixme: replace by views::cartesian_product
-  for (auto&& [a, b, c] : std::ranges::cartesian_product_view(v, v, v)) {
+  for (auto&& [a, b, c] : std::ranges::views::cartesian_product(v, v, v)) {
     out << a << ' ' << b << ' ' << c << '\n';
   }