[libcxx-commits] [libcxx] [libc++][ranges] implement `std::ranges::zip_transform_view` (PR #79605)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,99 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// constexpr auto end()
+// constexpr auto end() const
+//   requires range<const InnerView> &&
+//            regular_invocable<const F&, range_reference_t<const Views>...>;
+
+#include <ranges>
+
+#include "types.h"
+
+template <class T>
+concept HasConstEnd = requires(const T& ct) { ct.end(); };
+
+template <class T>
+concept HasEnd = requires(T& t) { t.end(); };
+
+constexpr bool test() {
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+  {
+    // simple test
+    std::ranges::zip_transform_view v(
+        MakeTuple{}, SimpleCommon{buffer}, std::views::iota(0), std::ranges::single_view(2.));
+    assert(v.begin() != v.end());
+    assert(std::as_const(v).begin() != std::as_const(v).end());
+    assert(v.begin() + 1 == v.end());
+    assert(std::as_const(v).begin() + 1 == std::as_const(v).end());
+  }
+
+  {
+    // with empty range
+    std::ranges::zip_transform_view v(MakeTuple{}, SimpleCommon{buffer}, std::ranges::empty_view<int>());
+    assert(v.begin() == v.end());
+    assert(std::as_const(v).begin() == std::as_const(v).end());
+  }
+
+  {
+    // common_range<InnerView>
+    std::ranges::zip_transform_view v(MakeTuple{}, SimpleCommon{buffer});
+    auto it       = v.begin();
+    auto const_it = std::as_const(v).begin();
+    auto st       = v.end();
+    auto const_st = std::as_const(v).end();
+
+    static_assert(!std::same_as<decltype(it), decltype(const_it)>);
+    static_assert(!std::same_as<decltype(st), decltype(const_st)>);
+    static_assert(std::same_as<decltype(it), decltype(st)>);
+    static_assert(std::same_as<decltype(const_it), decltype(const_st)>);
+
+    assert(it + 8 == st);
+    assert(const_it + 8 == const_st);
+  }
+  {
+    // !common_range<InnerView>
+    std::ranges::zip_transform_view v(MakeTuple{}, SimpleNonCommon{buffer});
+    auto it       = v.begin();
+    auto const_it = std::as_const(v).begin();
+    auto st       = v.end();
+    auto const_st = std::as_const(v).end();
+
+    static_assert(!std::same_as<decltype(it), decltype(const_it)>);
+    static_assert(!std::same_as<decltype(st), decltype(const_st)>);
+    static_assert(!std::same_as<decltype(it), decltype(st)>);
+    static_assert(!std::same_as<decltype(const_it), decltype(const_st)>);
+
+    assert(it + 8 == st);
+    assert(const_it + 8 == const_st);
+  }
+
+  {
+    // underlying const R is not a range
+    using ZTV = std::ranges::zip_transform_view<MakeTuple, SimpleCommon, NoConstBeginView>;
+    static_assert(HasEnd<ZTV>);
+    static_assert(!HasConstEnd<ZTV>);
+  }
+
+  {
+    // Fn cannot invoke on const range
+    using ZTV = std::ranges::zip_transform_view<NonConstOnlyFn, ConstNonConstDifferentView>;
+    static_assert(HasEnd<ZTV>);
+    static_assert(!HasConstEnd<ZTV>);
+  }
+  return true;
+}
+
+int main(int, char**) {
+  test();
----------------
ldionne wrote:

Same comments for 1, 2 and 3 will apply here. Also for the empty view in 0, 1 and 2 positions.

https://github.com/llvm/llvm-project/pull/79605