Re: objective-c: how slow ?

[Richard Frith-Macdonald]

On Saturday, September 8, 2001, at 01:36 AM, Marko Mikulicic wrote:

> > [snip]
> > > Objc has a simpler lookup because it doesn't have multiple 
> > > inheritance,
> > > delegation
> > Doesn't forwarding and DO count as delegation?
>
> Not really. Delegation uses the delegate to lookup the method
> but forwards the original receiver.
> (One example is better than a thousand words. see attachment)

Actually, what you are describing is not true delegation ...
Delegation is what is commonly done in ObjC - an object asks another
object to do a job for it.

The capability you are describing here is also possible using the
ObjC runtime (the GNUstep base library uses it in a few places), and
is called 'behaviors'.   The object takes on a behavior of another
object rather than delegating  to another object.

So, with delegation and object A which does not handle a particular
message, passes the message to a delegate object B which executes
the appropriate method, whereas with behaviors, A gets the method from
B and executes it itsself.

The behavior mechanism is not directly supported by the language, and
is therefore dangerous in ObjC - since you need to be careful not to
take on any behavior which would try to work with instance variables
that don't exist in your object and cause a crash.  In other languages
where ivars are only accessed by methods, you just need to worry about
runtime exceptions, not actual crashes when you make a mistake.