From: Olivier Renaud <o.renaud@...>
Date: 2007-02-20T20:45:55+09:00
Subject: Re: Help with Class design

> I think I understand what you mean, but I am so used to programming in
> languages where assignments are common place (eg. Matlab) that I am
> struggling to adjust to this new way of thinking. For example I have a
> method :
>
> def diff()
>     result = []
>     @signal.each_index do |i|
>       result << @signal[i+1] - @signal[i] unless i == (@signal.length -
> 1)
>     end
>     result
> end
>
> which takes a @signal object and returns an array of the differences
> between each successive element of signal. But now I cannot write
>
> a = MySignal.new([1,2,3])
> a.diff.variance
>
> because diff has returned an object of class "array" and the variance
> method is not defined . How do I write "diff" in someway that it gives
> me a new "signal" instead of an array ?
>
> Thank you all for your help !
>
> Chris

You want to return a new Signal so... just do it !

def diff()
    result = []
    @signal.each_index do |i|
      result << @signal[i+1] - @signal[i] unless i == (@signal.length-1)
    end
    return MySignal.new(result)
end

Maybe I missed something in your question, or maybe you would like your class 
MySignal to act more like an Array. If so, there are many solutions (in order 
of preference) :

* Use the Forwardable module to give access to specific methods from Array
* Use the Delegate lib to delegate all unknown methods to Array
* Make your class a subclass of Array (but delegation is almost always better)
* Reopen Array and add extra features (but this should be reserved for some 
specific needs, not in your case)

I hope I answered your question :)

-- 
Olivier Renaud