multiple `alias this` suggestion

[Carl Sturtivant via Digitalmars-d]

On Wednesday, 26 April 2017 at 15:00:30 UTC, Steven Schveighoffer 
wrote:
> I think you can appreciate that this doesn't scale. Imagine a 
> case which has 2 or 3 optional alias this items.
>
> -Steve

Agreed, not manually, as it is exponential in the number of 
conditions. But I think some template machinery could mixin the 
right stuff in one place avoiding that problem, implanting the 
existing names in an `alias this`. So
   AliasThis!(x,y,z)
which could detect if each name exists in an instantiation and 
only use that name if so, and would be placed outside of any 
`static if` to do the job.

I'm leaning toward the notion that a single AliasThis of the kind 
I suggested  with a suitable template library to help out with 
matters such as the one you raised is enough.

(Some name management for shadowed names could be in that library 
too --- different topic, will discuss elsewhere.)