From: "David A. Black" <dblack@...>
Date: 2008-06-15T03:40:51+09:00
Subject: Re: Knowing which subclass called a superclass class method

Hi --

On Sun, 15 Jun 2008, Rob Boellaard wrote:

> to continue on the same theme, if this is the class:
>
>
> class S
>
> puts "1" + self
>
>    def self.doSomething
>        puts "2" + self

Do you mean self.name, in both cases?

>    end
>
> end
>
>
> I get:
>
> 1 S
> 2 A

I assume that you've done:

   class A < S
   end

   A.doSomething # or do_something, using Ruby style naming

and that you didn't really get magically-inserted spaces :-)

>  why is there this difference? and is there a way to get A in the first
> case?

The code inside a class definition gets executed when the class
definition is read in. Code at the top level of the definition, like
your puts statement, gets executed right away. Method definitions get
executed in the sense that the methods get defined, but the methods
themselves don't get executed until they're called.

So your definition of S does two things:

   * prints out "1" + self.name
   * defines a method, to be called later

If you want to do the puts'ing for a subclass, you could do:

   class S
     def self.inherited(c)
       c.class_eval { puts "1" + self.name }
     end
   end

(or just puts "1" + c.name)


David

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