From: dblack@...
Date: 2006-01-09T11:20:22+09:00
Subject: Re: Adding a method to a single object

Hi --

On Mon, 9 Jan 2006, Marco Lange wrote:

> Hi,
>
> how is it possible to add a method to a single object programatically?

def obj.meth
   ...
end

(and a few other ways, but that's the simplest)

> E.g. I want to write a method
>
> class Object
>
>  def rename_method(old_id, new_id)
>    ...
>  end
>
> end
>
> The method shall rename a method for a specific instance of any class, e.g. 
> the following should be possible:
>
>
> a = 5
> 5.rename_method :times, :veces
>
> 5.times { ... }
>  -> Error, Method "times"does not exist
>
> 5.veces { ... }
>  -> Expected behaviour
>
> I already succeeded in renaming methods for whole classes, but for a single 
> instance?

Keep in mind that a single instance has a class of its own -- its
singleton class -- as well as its class of origin.  If you do the
renaming in the singleton class, it will affect only that object.

Have a look at this example, and see if it helps:

   class C
     def m
       puts "In the method"
     end
   end

   c = C.new
   c.m   # In the method

   class << c   # "<< c" invokes the singleton class of c
     alias n m
     undef_method("m")
   end

   c.n  # In the method
   c.m  # error -- no such method

Hmmm... one problem is that Fixnums don't have singleton classes, so
this wouldn't work for 5.  Anyway, maybe it will give you ideas :-)


David

-- 
David A. Black
dblack@wobblini.net

"Ruby for Rails", from Manning Publications, coming April 2006!
http://www.manning.com/books/black