Improve a simple event handler

[JN]

On Saturday, 15 January 2022 at 23:15:16 UTC, JN wrote:
>
> Is there some way I could improve this with some D features? My 
> main gripes with it are:
>

Managed to dramatically simplify it to 10 lines of code with 
variadic templates.

```d
import std.stdio;

struct Event(T...)
{
     void function(T)[] listeners;

     void addListener(void function(T) handler)
     {
         listeners ~= handler;
     }

     void emit(T args)
     {
         foreach (listener; listeners)
         {
             listener(args);
         }
     }
}

void onResize(uint newWidth, uint newHeight)
{
     writefln("Resized: %d %d", newWidth, newHeight);
}

void main()
{
     Event!(uint, uint) windowResizeEvent;
     windowResizeEvent.addListener(&onResize);

     windowResizeEvent.emit(1000, 2000);
}
```

I am very happy with this solution.