Dispatching values to handlers, as in std.concurrency

["Luís]

On Monday, 6 May 2013 at 23:53:51 UTC, Idan Arye wrote:
> If the type handlers are your own classes, then you can let 
> them check it. Have a method in the handlers that check if an 
> object can be handled by that handler, and use it on each 
> handler until you find one that fits.

I don't understand. Imagine I have:

     class X
     {
         void handleFoo(Foo msg) { ... }

         void handleBar(Bar msg) { ... }
     }

I want to register an instance of X to receive messages of type 
Foo (or subclass) and messages of type Bar (or subclass) in the 
respective handler methods. Where are you proposing for your 
check to be implemented?