From: benjohn@...
Date: 2007-02-20T21:26:54+09:00
Subject: Re: Help with Class design

>> What you're trying to do with inject is make a more "functional"
>> program; you're trying to avoid assigning to things; you're closer to
>> saying what you want done, rather than how you want it done
>> (declarative
>> verses imperative style). If you start making assignments, you break
>> away from that style.
>
> 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 ?

Get it to wrap the array in to a signal, and return that.

So, at the end of the method you'll do something like:

  ...
  end
  Signal.new(result)
end

Cheers,
  Benj