[libcxx-commits] [libcxx] [libc++] Resolve LWG4308, correct `iterator` availability for `optional<T&>` (PR #173948)

[A. Jiang via libcxx-commits]

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frederick-vs-ja wrote:

I don't think we should use `__val` in a test file. Pedantically speaking, it makes user code ill-formed, no diagnostic ([[lex.name]/3](https://eel.is/c++draft/lex.name#3)). Perhaps it's better to use `V` or `Val`.

https://github.com/llvm/llvm-project/pull/173948