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

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,63 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 iterator(iterator<!Const> i)
+//     requires Const && convertible_to<ziperator<false>, ziperator<Const>>;
+
+#include <ranges>
+
+#include <cassert>
+
+#include "../types.h"
+
+using ConstIterIncompatibleView =
+    BasicView<forward_iterator<int*>,
+              forward_iterator<int*>,
+              random_access_iterator<const int*>,
+              random_access_iterator<const int*>>;
+static_assert(!std::convertible_to<std::ranges::iterator_t<ConstIterIncompatibleView>,
+                                   std::ranges::iterator_t<const ConstIterIncompatibleView>>);
+
+constexpr bool test() {
+  int buffer[3] = {1, 2, 3};
+
+  {
+    std::ranges::zip_transform_view v(MakeTuple{}, NonSimpleCommon{buffer});
+    auto iter1                                       = v.begin();
+    std::ranges::iterator_t<const decltype(v)> iter2 = iter1;
+    assert(iter1 == iter2);
+
+    static_assert(!std::is_same_v<decltype(iter1), decltype(iter2)>);
+
+    // We cannot create a non-const iterator from a const iterator.
+    static_assert(!std::constructible_from<decltype(iter1), decltype(iter2)>);
+  }
+
+  {
+    // underlying non-const to const not convertible
----------------
ldionne wrote:

```suggestion
    // Check when we can't perform a non-const-to-const conversion of the ziperator
```

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