Support 'to_wstring(T)' in module.

[DanielaE]

FMT_STRING(x) doesn't work in modules yet because of FMT_STRING_IMPL. In this particular case, this alternative implementation might even be superior?

[alexezeder]

Is it the only place where FMT_STRING cannot be used with modules? For example, FMT_STRING also used in ranges.h:

fmt/include/fmt/ranges.h

Line 364 in 84a36b9

out = format_to(out, FMT_STRING("{}"), " ... <other elements>");

FMT_STRING(x) doesn't work in modules yet because of FMT_STRING_IMPL

Does it mean that you want to make it work in the future? 🙂
IMHO, it's not worth it, as well as FMT_COMPILE, since you also mentioned that macro here:

The macro-based interfaces FMT_STRING and FMT_COMPILE are not yet implemented. Macros cannot get exported from modules.

As far as I can see, there is no need to export FMT_COMPILE macro from {fmt} module because _cf literal makes it obsolete.

It's a little more complicated with FMT_STRING - there is no literal for that. Still, there are (or will be, IDK, @vitaut knows it better) Compile-time format string checks by default that has one flaw (as I see it) - no other option but to have implicit fallback without checks for non-statically named arguments. FMT_STRING doesn't have this flaw because it handles this explicitly.

Aside from the concern with FMT_STRING, looks like {fmt} module can be fully functional without these macros. So probably macro-based interface can just be omitted. What do you think?

[DanielaE]

At present, ranges.h is not part of modularized {fmt}.

I do have an implementation of FMT_STRING and FMT_COMPILE which is based on udl-based compile-time literal arguments. I still haven't looked into possible other solutions like immediate functions. Unfortunately, the current implementation is not yet supported in msvc's modules implementation (may be 16.10-pre3 will do). Even more unfortunately, no other compiler is even able to survive attempts to compile fmt.cc. Without the modules-related lines in there, every compiler should be fine and compile {fmt} into a single object file, with them an advanced compiler chould create a BMI, too.

[vitaut]

Thanks for the suggestion but don't think it's necessary since this is an internal use of FMT_STRING that doesn't require this macro to be exported.