From: Markus <markus@...>
Date: 2004-10-06T03:12:35+09:00
Subject: Re: A ruby course

On Tue, 2004-10-05 at 10:24, Brian Schr旦der wrote:
> Hello Group,
> 
> I need more help.
> 
> Anybody has an idea for an exercise on extending existing classes. So 
> far the only thing I have come up with is:
> 
> \exercise{Fibonacci II}{
>    Extend \codetype{Integer} with a function fib that calculates the
>    corresponding fibonacci number.}
> 
> And my creativity is at an all time low.

      * Sub class (or extend) array to support "card deck" semantics,
        e.g. cut, shuffle, deal, and (*smile*) maybe even stack?

      * Add set-like operations to hash (e.g. &&, ||)

      * Here's one I find this very useful: add aggregate behaviour to
        hashes.  For example have { :a=>3, :b=>[0,5,2], :c=>8 } +
        {:b=>[7], :c=>4} return { :a=>3, :b=>[0,5,2,7], :c=>12 }

      * Add some sort of simple substitution cypher to String


> > p52. It would be good to teach extending objects, because it's core to
> >      Ruby, and important when understanding "class methods".  But you
> >      can emphasise that it's advanced material, so students needn't be
> >      worried if they don't get it straight away.  (It's not *that*
> >      hard to accept, anyway... :)
> > 
> 
> Anybody nows of a good example where it is neccessary to extend an 
> existing object?

As far as I'm concerned, things like:

def Symbol.intern
     self
     end

but I don't think that's quite what your asking.

> I have never used this feature and I don't know when to use it in a 
> sensible way.

     If you're talking about extending individual objects, the only time
I can recall using it extensively was in a little text based adventure
game.  It's kind of odd now that I think about it: I love the ability
but I use it very sparingly. 

> > p55. Missing exercises.
> 
> Somebody has an idea for an exercise on using modules (as namespace and 
> mixin?)

     A linked list or tree package is the semi-standard answer.  You can
add it to any class & do "classical" lists & trees.  You may want to
note that this isn't very rubyesque thought.
     Maybe a simple version history "memento" setup?  Or taint tagging
with more history/details than tainted or not?  Or some sort of math
package (& use this to introduce Math)?


     -- Markus