From: Sean Middleditch <elanthis@...>
Date: 2002-01-16T01:43:18+09:00
Subject: RE: benefits of callbacks

Signals.  You can register a function (or an object, in Ruby) to listen
to a particular function in another object.  Then, when said signal is
generated, the callback is activated.

The place this is most commonly used is a GUI.  For example, you can
register an object to be called when a user signal is generated (user
clicked on OK button).

Without callbacks, you'd have to, for ever GUI object, make a child
object with some form of "activate" method or something, which would be
more complex (depending on the exact situation).  And then, on top of
that, only the child object could respond - if you need multiple
sections of code to be updated when a signal is generated, it wouldn't
be possible without callbacks (or some really really ugly code).

Another way to look at callbacks is the way Ruby allows you to
dynamically change a method in an object.  This is, really, just another
form of callbacks.  Setting the method is analogous to registering a
callback; when the object invokes the method, it's just like calling a
callback.  Of course, setting a method of an object is limited in that
you can only have *one* callback registered for a particular purpose at
a time...

On Tue, 2002-01-15 at 11:31, Jack Dempsey wrote:
> Ok, but being in Ruby (which most certainly is OO =P), why are callbacks so
> useful?
> 
> Thanks!
> Jack
> 
> > -----Original Message-----
> > From: Ralph Mason [mailto:ralph.mason@telogis.com]
> > Sent: Tuesday, January 15, 2002 2:47 AM
> > To: ruby-talk ML
> > Subject: Re: benefits of callbacks
> >
> >
> > A callback gives the power of a virtual or late binding function
> > to a non OO
> > language.
> >
> > Will that do?
> >
> > Ralph
> >
> > ----- Original Message -----
> > From: "Jack Dempsey" <dempsejn@georgetown.edu>
> > To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
> > Sent: Tuesday, January 15, 2002 8:10 PM
> > Subject: benefits of callbacks
> >
> >
> > > A co-worker asked today what they were and why they are so
> > useful, and to
> > be
> > > honest, I struggled in giving a good example. Anyone have a sec
> > to spare?
> > >
> > > Thanks!
> > > Jack
> > >
> > >
> >
> >
>