From: David Alan Black <dblack@...>
Date: 2002-05-04T12:50:46+09:00
Subject: Re: Adding new method to Built-In class

Hello --

On Sat, 4 May 2002, Hubert Hung-Hsien Chang wrote:

> I have tried to add new method to built-in class without success.
> In other words, I do not want to have instance method, expression method
> and I do not want to create a new class as a subclass just to add this
> new method.
>
> I want to add to the build-in class by (some how)
>
> def String.new_method
>     print "give me a method!"
> end
>
> But this 'new_method' won't work on any instance other than
> calling it by itself. In other words,
>
> a = 'test string'
> a.new_method
>
> only produces error.
>
>
> So any idea?

What you need to do is re-open the class String, and define a new
instance method:

  class String
    def new_method
      puts "give me a method!"
    end
  end

  "abcde".new_method  # =>  give me a method!

Doing it that way will cause every string object to respond to that
method.  With what you originally did, you actually added a class
method to String:

    def String.new_method
      puts "give me a method!"
    end

    String.new_method  # =>  give me a method!

... so in that case, the object that responds to new_method is the
class String itself, rather than individual strings.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav