Mimicking Java's Type Erasure

[Superstar64]

On Monday, 4 November 2019 at 01:25:36 UTC, Heromyth wrote:
> 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);
I don't think you understood my question.
Your `shout.show(type,that)` expression wouldn't compile because 
you can't have you can't have a templated virtual function in an 
interface(a rank 2 type).

What I'm asking if there is a way to take a rank 1 type and 
create a delegate to it.

``
string show(A)(string delegate(A) callback, A that){
     // ...
}

void main(){
     // borrow haskell's syntax for a minute
     (forall A. string delegate(string delegate(A),A)) shower = 
show;
     show(a => a,"hello").writeln;
}
``
Now I understand this isn't possible natively possible because of 
how D's templates works, but I'm asking if there's a good 
workaround to replicate that behavior.