From: Robert Klemme <shortcutter@...>
Date: 2009-03-21T01:37:15+09:00
Subject: Re: self.inherited but wait until subclass is fully defined?

On 20.03.2009 17:22, matt neuburg wrote:
> Howdy. I am a class. There are certain rules for what you are supposed
> to do when you subclass me, so as a sanity check I wish to introspect
> your subclass to make sure it's obeying the contract.
> 
> However, my problem is that self.inherited is called too early.
> 
> class C # this is me
>  def self.inherited(p)
>   #whatever
>   super
>  end
> end
> 
> class B < C # this is you
> # C's self.inherited is called right here
>  def yourFirstMethod
>   # etc.
>  end
> end
> 
> So I can't, in my self.inherited, ask about what methods you have
> defined, because you haven't defined them yet. This must have come up
> before; is there an easy solution? Thx - m.

Even after the class definition methods can be added.  You could catch 
that with method_added but if you require a minimum set of methods to be 
defined before class is used (e.g. instantiated) this will be difficult 
to track.  One option would be to define method initialize in your class 
and do the check there.  But this is still fragile because it might not 
be guaranteed that sub classes invoke it from their initialize...

Another option would be to override the sub class's method "new" so you 
can do the check there.  This might be a bit more robust but even "new" 
can be overridden by subclasses (although it isn't generally).

I'd probably just omit the check.  If any of your superclass methods 
invokes a method that is not defined you'll see this at runtime anyway.

Kind regards

	robert