On Feb 22, 2007, at 11:46 PM, Göran Krampe wrote:
> As most people know a java interface is a "named bunch of messages"  
> that a
> class (or its superclasses of course) can declare it implements.  
> But this
> is early binding, right?
>
> I would be more interested in "late" binding where I could do:
>
>    someThingy respondsToProtocol: aProtocol
>
> ...where aProtocol is more or less just a bunch of selectors. The main
> difference is of course that the class (or any of its superclasses) of
> someThingy doesn't need to *declare* that it implements aProtocol - it
> just has to actually do it. :)
>

Get a mac. :-)

ObjectiveC  has Protocols (which I think were the inspiration for  
Java's interfaces). Protocols can be formal (the class declares it  
implements a protocol explicitly and the compiler whines if you leave  
something out) or informal - you implement it but you don't declare it.

There is a lovely method in Cocoa conformsToProtocol: that does just  
what you're asking.  I don't know how it works, but if I were to  
implement such a thing in Squeak in a cheap and cheerful way - I  
would reify a protocol as a class  and attache protocols to existing  
classes much the way PoolDictionaries work now only instead of  
importing shared constants, you are using it to enforce a set of  
methods.  How tools prompt you to make sure you conform to the  
protocol you declare is an exercise left to the implementer.

-Todd Blanchard