DIP66 - Multiple alias this

[Paolo Invernizzi]

On Wednesday, 30 September 2020 at 01:36:59 UTC, Mike wrote:
> On Monday, 28 September 2020 at 19:55:10 UTC, Andrei 
> Alexandrescu wrote:
>
> 1.  Deprecate `alias this` for classes, and implement multiple 
> `alias this` for structs.  That will give users the composition 
> feature they need, and in addition, because structs cannot 
> inherit, it removes the complexity Walter spoke of.

This!

We've never used alias this for classes, I'm wondering if there's 
something like that in Phobos, or in other projects ...