On 08/12/2023 07.46, Yongwei Wu via Std-Discussion wrote:
> There are quite a few specialization points in the std namespace that
> a user-defined type can leverage, e.g.:
>
> - std::hash (for use as key in the unordered associative containers)
> - std::is_error_code_enum (to act like an error code)
> - std::tuple_size and std::tuple_element (to be tuple-like)
>
> Unfortunately, specialization of such templates requires quitting the
> current namespace and adding specialization at the global or std
> namespace, which is extremely inconvenient.

> Another issue Mike mentioned was how names should be resolved in the
> specialization: should we choose first a symbol in the "current"
> namespace, or a symbol in the "specialized" namespace? I do not hold a
> strong opinion here, but either solution seems better than having to
> exit to the global namespace.

And, as far as I remember, this is the main pain point:
Which lookup rules do we pick?

Obviously, that needs to be a considered decision, with some analysis
in a paper.

Jens