How would you implement this in D? (signals & slots)

[Chris Wright via Digitalmars-d-learn]

On Tue, 02 Feb 2016 15:59:06 +0000, Atila Neves wrote:
> struct String1 { string s; }
> struct String2 { string s; }

I've seen this sort of thing before. A blogger I used to follow, Jeremy 
Miller, implemented an event broker using this pattern. I don't like it. 
It requires a new type for each event, and you have to defensively use 
that pattern even if you only have one event at the moment. Every time I 
implemented an event system, I've gone with named events and no special 
type for their parameters.

With std.signals, you could do this:

struct Event(TArgs...) {
  mixin Signal!TArgs;
}

class Foo {
  Event!string usernameEntered;
  Event!string passwordEntered;
  Event!(long, string) someOtherEventHappened;
  void enterPassword(string s) { passwordEntered.emit(s); }
  void enterUsername(string s) { usernameEntered.emit(s); }
}

void main() {
  auto o = new Observer;
  auto f = new Foo;
  f.usernameEntered.connect(&o.watch);
  f.passwordEntered.connect(&o.watch);
  f.enterUsername("adelhurst");
  f.enterPassword("********");
}