hasStaticMember and enums

Aliak something at something.com
Tue Sep 22 04:50:01 UTC 2020

On Monday, 21 September 2020 at 23:33:17 UTC, Steven 
Schveighoffer wrote:
> I was confused today when I was looking to see if a particular 
> field name was a field of a struct and not a static member.
> I thought __traits(hasMember, T, item) && !hasStaticMember!(T, 
> item) would suffice. But then I found that this returns true 
> for enums that are part of the type.
> struct S
> {
>    enum e = "hello";
> }
> static assert(__traits(hasMember, S, "e"));
> static assert(!hasStaticMember!(S, "e"));
> The reason is because hasStaticMember ultimately uses:
> alias sym = Alias!(__traits(getMember, U, member));
> ...
> enum hasStaticMember = __traits(compiles, &sym);
> which of course doesn't compile for an enum.
> But I would actually consider an enum to be a static member. 
> It's a member, but does not consume any part of the instance.
> The docs for hasStaticMember are pretty slim, but it was added 
> here: https://github.com/dlang/phobos/pull/5112
> There is no mention of how this should play with enums. Would 
> it be bad to add a check for enums in this? I was thinking of 
> changing the __traits(compiles) line to:
> __traits(compiles, (auto ref a) { } (sym));
> or something like that.
> Thoughts?
> I'm also not sure why std.meta.Alias is used instead of a 
> normal alias (maybe that used to be an issue? I tried just a 
> straight alias and it works at least in this case).
> -Steve

Thoughts: static members are addressable so if you have metà 
programs that are checking if something is static and then taking 
the address based on that, those will break. So they are the same 
in how you access them but not in terms of memory.

Can there be a different meta function that checks for static, 
non-static, and manifest? “HasAnyMember”?

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