From: Eric Mahurin <eric.mahurin@...>
Date: 2006-08-26T22:25:23+09:00
Subject: Re: Duck typing alows true polymorfisim

------=_Part_78786_28301241.1156598722538
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

On 8/25/06, atbusbook@aol.com <atbusbook@aol.com> wrote:
>
> lets say you want a generic numerical algorithom like sum
>
> Ruby
>
> def sum lst
>   lst.inject(0){|total,current| total*current}
> end
>
> Java // i dont know if there is a numeric super class for numbers
>
> class Sum{
>   public static int sum(int[] lst){
>     int total = 0;
>     for(int current : lst){
>       total+=current;
>     }
>     return total;
>   }
>   // repeat for all other number types
> }
>

The title of this thread was almost like a post I made a year or so ago:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/145049

What you wrote still isn't as generic as it could be.  This can handle more
than just numerics:

def sum enum
  enum.inject{ |total,current| total+current }
end

enum can be anything that responds to inject (likely an Enumerable) with a
block that takes 2 arguments where the first responds to +.  If enum is an
Enumerable, this means the first element responds to + which returns
something that also continues to respond to +.

Now you can do this:

three = sum([1,2])
hello_world = sum(["hello","world"])
concatenated_lines = sum(anIO)

The simpler you can make the description of the duck-typing of a method, the
more generic and flexible it will be.  By adding a 0 argument to inject, you
made the duck-typing a little more complex and stiffled it by only allowing
elments that can be added to 0.

------=_Part_78786_28301241.1156598722538--