From: dblack@...
Date: 2006-01-09T22:04:06+09:00
Subject: Re: Ideas on "Why Living Dangerous can be A Good Thing" in Ruby?

Hi --

On Mon, 9 Jan 2006, Steve Litt wrote:

> On Sunday 08 January 2006 06:14 pm, dblack@wobblini.net wrote:
>>
>> I'm not sure what you mean by adding an instance variable to a class,
>> but as for methods, they're all defined at runtime.
>>
>>    class C
>>      def m
>>      end
>>    end
>>
>> That code gets executed, and then there's a class called C with an
>> instance method m.
>>
>> I'm not sure what it is that you consider subclassing to be a better
>> choice than.  Are you talking about define_method?  Or the practice of
>> reopening core classes?
>>
>>
>> David
>
> Hi David,
>
> I don't know for sure, because when I read about this stuff my first reaction
> was "I'm not gonna do that!"
>
> I got the impression I could do this:
>
> myclass = MyClass.new
> myclass.never_seen_before_attribute = 5
>
> As I said, I didn't research it because I considered its use to be a negative,
> but stored it in the back of my mind in case I had to maintain code like
> that.

I think you mean method_missing.  It has nothing to do with instance
variables; it's just a hook or callback that you can define to
intercept calls to non-existent methods.  What you do at that point is
up to you.  You can also just not define it, in which case a call to a
non-existent message will raise an exception.

There's nothing inherently dangerous or non-deterministic about
method_missing.  It's basically a control-flow technique.


David

-- 
David A. Black
dblack@wobblini.net

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