RBTree delegates and types

[Viktor]

On Monday, 19 March 2018 at 11:30:13 UTC, Steven Schveighoffer 
wrote:
> Yes, you need a `this` pointer for it to work. However, we can 
> do this by encapsulating the return type with an auto function:
>
> https://run.dlang.io/is/inSzaU
>
> Sorry I didn't get this right away. Interesting chicken-and-egg 
> problem, but as usual, D delivers :)
>
> -Steve

That's beautiful! Thanks!