Implementing interfaces using alias this

[Balagopal Komarath via Digitalmars-d-learn]

On Wednesday, 14 June 2017 at 21:04:55 UTC, basile b. wrote:
> The way to do that in D is with mixins:

That is an interesting solution.

However, my original goal was to figure out whether one can make 
struct types behave polymorphically (Which is not mentioned in my 
original question).  I know that this is not supported by design. 
I want to keep the original struct types but also allow functions 
to accept those struct types and do runtime dispatch. The 
following code should give a better idea by what I mean by this.

https://dpaste.dzfl.pl/051f6a4da059

The user need only define Duck1, Duck2 ... with appropriate 
functions and mixin toDuck. Then a function that accepts a Duck 
can accept DuckLike (for dynamic dispatch) or templatize on the 
type of Duck.