Fix udl_compiled_string with non-byte chars (e.g. wchar)

[alexezeder]

Without this fix, udl_compiled_string works only for char types that have a 1-byte size.

[DanielaE]

This is totally fine. I did exactly the same in a different context outside of UDLs.

[vitaut]

Can we move remove_cvref_t<decltype(Str.data[0])> to a default template parameter to avoid repetition? i.e.

template <detail::fixed_string Str, Char = remove_cvref_t<decltype(Str.data[0])>>

[alexezeder]

Looks like it's not possible because compilers expect to see certain template arguments - https://godbolt.org/z/6odY6E78h

[vitaut]

Can we at least do typename Str::char_type?

[denchat]

How about value_type as in basic_string<>::value_type ?

[vitaut]

Sure, value_type is a more appropriate.

[alexezeder]

Don't forget that Str is not a type, it's an object since it's passed as a non-type template parameter, so we have these options here:

<remove_cvref_t<decltype(Str.data[0])>, sizeof(Str.data) / sizeof(decltype(Str.data[0])), Str>
vs.
<typename decltype(Str)::value_type, sizeof(Str.data) / sizeof(typename  decltype(Str)::value_type), Str>

and they both are not great.

But the size of fixed_string can be exposed by a static member or function, like so:

<typename decltype(Str)::value_type, decltype(Str)::size, Str>

Just let me know if this approach is preferable.

[vitaut]

I think it's fine as is then. Thanks for the fix.