I implemented delegates in D

[maik klein via Digitalmars-d]

I am currently writing a task system and I have this case where I 
want to send a delegate to a different thread but this delegate 
also captures a variable. I use this to implement a "future".

Now as far as I know this delegate will allocate GC memory and I 
just wanted to avoid that, just for fun.

Here is the code https://dpaste.dzfl.pl/cd77fce99a5b

I have only worked on it a couple of hours and I am sure there 
are many problems with it.

Basically the idea is that you can use normal lambda syntax. If 
you want a function that returns and int and takes an int, you 
can write it like this:

(int i) => i

If you want a function that returns an int, takes an int, but 
also captures and int you would write it like this

(int i, int captured) => i + captured

But you also have to declare the base function type without the 
captured variables beforehand.

Fn!(FnType!(int, int), (int i, int captured) => i + captured)(42);

That is how I know what the captured variables are.

The only part that is currently missing are polymorphic 
delegates. They are not too useful if I can't pack them into the 
same array.

I guess I have to do this with classes/interfaces.

Thoughts?

Has this been done before?