Re: Using __traits(getMember...) in alias statement

[Timon Gehr]

On 11/17/2011 06:12 PM, Tobias Pankrath wrote:
It would be cool, if the following would be possible.
----
immutable string MemberID = "M";
struct A {}
struct B {
     alias A M;
}

template Member(T)
{
     static if(__traits(hasMember, T, MemberID))
     {
         alias __traits(getMember, T, MemberID) Member;
     }
     else
         alias TypeTuple!() Member;
}

void main()
{
     alias Member!(B) M;
}
----

Currently dmd will print "basic type expected, not __traits".
Why isn't traits allowed here and if we allow __traits there, would this
introduce any ambiguities?


This works:

alias TypeTuple!(__traits(getMember, T, MemberID)) Member;

It is a mere grammar issue. The aliased symbol must look like a valid 
type. I'd like that to change too.

This helps a lot with the current state of affairs:

template ID(alias x){alias x ID;}


It will even allow funny things like this:

alias ID!((a,b){return a+b;}) add;

static assert(add(1,2) == 3);