[libcxx-commits] [libcxx] [libc++][ranges] Fix missing `forward` in `views::enumerate` (PR #197635)

[A. Jiang via libcxx-commits]

================
@@ -90,6 +90,26 @@ static_assert(!std::is_invocable_v<decltype(std::views::enumerate), NotInvocable
 
 static_assert(std::is_same_v<decltype(std::ranges::views::enumerate), decltype(std::views::enumerate)>);
 
+struct MoveOnlyView : std::ranges::view_base {
+  constexpr explicit MoveOnlyView(int* b, int* e) : begin_(b), end_(e) {}
+  MoveOnlyView(const MoveOnlyView&)            = delete;
+  MoveOnlyView& operator=(const MoveOnlyView&) = delete;
+  constexpr MoveOnlyView(MoveOnlyView&& other) : begin_(other.begin_), end_(other.end_) {
+    other.begin_ = nullptr;
+    other.end_   = nullptr;
+  }
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frederick-vs-ja wrote:

Nitpick: Let's improve this move ctor with `exchange` and add conventional `noexcept` to it.
```suggestion
  constexpr MoveOnlyView(MoveOnlyView&& other) noexcept
      : begin_(std::exchange(other.begin_, nullptr)), end_(std::exchange(other.end_, nullptr)) {}
```

https://github.com/llvm/llvm-project/pull/197635