From: Stefano Crocco <stefano.crocco@...>
Date: 2007-10-04T20:04:23+09:00
Subject: Re: (Newbie) Override * on Array

Alle giovedì 4 ottobre 2007, Mike Ho ha scritto:
> Hi,
>
> I've written a simplistic override of the * operator for Arrays so that
> [2,4,6]*[2,2,2] = [4,8,12]
>
> class Array
>
>   def *(other)
>
>     each_with_index do |x,i|
>       self[i]= x * other[i]
>     end
>   end
>
> end
>
> It assumes that the arrays are the same length and no error checking is
> done.
>
> My questions are; is this idiomatic Ruby?
> What solution  would an experienced Rubyist offer?
> How would it be best to handle exceptions when the arrays are of
> different dimensions and/or length?
>
>
> Many Thanks
>
> Mike

Usually, operators don't modify the operands, but return a new object with the 
result. For instance:

irb: 001> a1 = [1, 2 ,3]
[1, 2, 3]
irb: 002> a2 = [4,5]
[4, 5]
irb: 003> a1 + a2
[1, 2, 3, 4, 5]
irb: 004> a1
[1, 2, 3]
irb: 005> a2
[4, 5]

Your method, instead, modifies the first operand:

a1 = [1,2,3]
a2= [4,5,6]
a3 = a1*a2
p a1
=> [4, 10, 18]
p a3
=> [4, 10, 18]

I'd do it this way:

class Array

  def *(other)
    res = []
    each_with_index do |x,i|
      res[i]= x * other[i]
    end
    res
  end

end

or 

require 'generator'

class Array

  def *(other)
    SyncEnumerator.new(self, other).map{|x, y| x*y}
  end

end

Regarding errors, you I think you can check the size of the two array at the 
beginning of the method and raise TypeError if they're different.

I hope this helps

Stefano