Mimicking Java's Type Erasure

[Heromyth]

On Monday, 4 November 2019 at 00:16:53 UTC, Superstar64 wrote:
> Consider the following Java code.
> --
> import java.util.function.Function;
> public class Main{
>
>     //basic Rank2 type
>     static interface Stringer{
>         <A> String show(Function<A,String> type, A that);
>     }
>
>     static class Say implements Stringer {
>         public <A> String show(Function<A,String> type, A that){
>             return type.apply(that);
>         }
>     }
>
>     static class Shout implements Stringer {
>         public <A> String show(Function<A,String> type, A that){
>             return type.apply(that) + "!!!";
>         }
>     }
>
> }
> --
> This uses Java's generics' type erasure to create a basic rank 
> 2 type.
> What are some clean ways to implement something similar in D, 
> in a type safe manner if preferable?

String show(A)(Stringer stringer, Function<A,String> type, A 
that) {
        Shout shout = cast(Shout)stringer;
        if(shout !is null) {
              shout.show(type, that); return;
        }

        Say say = cast(Say)stringer;
        if(say !is null) {
              say.show(type, that); return;
        }

       assert(false, "Unsupported");
}

Stringer stringer = new Shout();
stringer.show(type, that);