From: "David A. Black" <dblack@...>
Date: 2005-04-04T21:29:41+09:00
Subject: Re: alias to module methods or class methods

Hi --

On Mon, 4 Apr 2005, Geert Fannes wrote:

> Hello,
>
> I tried to fix the Math.sqrt() domain error on windows I reported an
> hour ago by redefining the Math.sqrt method:
>
> module Math
>
>  alias sqrt_old sqrt
>
>  def Math.sqrt(x)
>
>    begin
>
>      Math.sqrt_old(x)
>
>    rescue Errno::EDOM
>
>      return 0.0/0.0
>
>    end
>
>  end
>
> end
>
>
>
> But this does not work. Apparently, I cannot create an alias to a module
> method. I tested a bit and found out I could not create aliases to class
> functions either. How can I create aliases to module methods and class
> methods?

You have to make the change in the class where the method is defined.
Class and module methods are basically singleton methods -- that is,
methods defined inside the singleton class of a particular object.  In
this case, the object is the Module object "Math" -- so you need to
open up the singleton class of Math:

   class << Math
     alias sqrt_old sqrt
     def sqrt(x)
       Math.sqrt_old(x)
     rescue Errno::EDOM
       return 0.0/0.0
     end
   end

(Note that a method definition gives you an implicit begin/end block,
so you don't need to write one inside the method.)


David

-- 
David A. Black
dblack@wobblini.net