[libcxx-commits] [libcxx] [libc++] Implement LWG3133: Modernizing numeric type requirements (PR #208145)

[A. Jiang via libcxx-commits]

https://github.com/frederick-vs-ja requested changes to this pull request.

I think we need further changes and test coverage.

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> - No code changes were needed for `std::valarray<T>`: its `operator[]` already indexes through a raw pointer and never relies on a user-overloadable `operator&`, so it already conforms to the revised wording.

However, I think we should still test this. I think we can use `operator_hijacker` from `operator_hijacker.h` to verify this, and add test cases to

- `libcxx/test/std/numerics/numarray/template.valarray/valarray.access/access.pass.cpp`
- `libcxx/test/std/numerics/numarray/template.valarray/valarray.access/const_access.pass.cpp`

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Moreover, if we do want reject instantiating `valarray` and `complex` with incorrect types, we should `static_assert` all syntactic requirements in "_Cpp17DefaultConstructible_, _Cpp17CopyConstructible_, _Cpp17CopyAssignable_, and _Cpp17Destructible_".

This would be lengthy but implementable. Please be aware of rvalues and non-const lvalues.

Also, we can use `(void)sizeof(std::valarray<T>);` for "pure" instantiation of the class template specialization, which should ensure that we won't reject instantiation too late.

https://github.com/llvm/llvm-project/pull/208145