How to do reflection on alias symbols

[Jonathan M Davis]

On Thursday, November 16, 2023 3:03:25 AM MST Arafel via Digitalmars-d-learn 
wrote:
> Hi all,
>
> Please consider the following currently non-working code:
>
> ```d
> struct bar {
>      public alias pubInt = int;
>      private alias privInt = int;
> }
>
> static foreach(member ; __traits(allMembers, bar)) {
>      // Error: argument `int` has no visibility
>      pragma(msg, __traits(getVisibility, __traits(getMember, bar, member)));
> }
> ```
>
> Is there any way to get the visibility, or more generically to reflect
> on an alias member as itself and not as the symbol pointed to without
> resorting to nasty __trait(compiles,...) tricks that fail more often
> than not?

Someone may be able to give you some advice on how to better deal with this
problem, but in general, aliases don't really exist as far as the compiler
is concerned. They get translated to the original type and handled that way
rather than treated as a separate type that translates to another type. They
exist enough that you can do stuff like give them different visibility
attributes for the original symbol, but that pretty much just affects
whether you can use the alias, and then it gets replaced with the real thing
immediately. As it is, IIRC, it was previously the case that there were bugs
where visibility attributes did not affect aliases properly, so it's not at
all surprising if there isn't a good way to access the visibility attribute
of the alias itself.

I would suggest that you open up a bug report for it -
https://issues.dlang.org - and certainly, there's a good argument that what
you're seeing here is a bug. I fully expect that what you're trying do just
wasn't properly considered previously and thus was not dealt with properly
when the other bugs for visibility attributes on aliases were fixed however
many years ago that was now. I very much doubt that what you're seeing is
the intended behavior - or at least I fully expect that if Walter or one of
the other compiler devs sees the issue, they will agree that what you're
trying to do should work.

- Jonathan M Davis