DIP66 v1.1 (Multiple) alias this.

[via Digitalmars-d]

On Monday, 3 November 2014 at 15:39:42 UTC, IgorStepanov wrote:
> I meant that when you say that X is a subtype of T and X is a 
> subtype of V where you don't know what T and V are, it means 
> you don't really know what you're doing. And that is an error 
> and the compiler should inform you about it as soon as 
> possible. However I may be mistaken.

IMO the behaviour should be analogous to name lookup for modules: 
there should be an error only on use. It's hard to come up with a 
non-artificial example, but I can imagine there are some valid 
use cases in generic code. It won't hurt to report the ambiguity 
error on use, while it could theoretically hurt to report it 
early, so I'd suggest to go with the former.