From: Logan Capaldo <logancapaldo@...>
Date: 2006-05-13T04:42:29+09:00
Subject: Re: final/closed classes in Ruby (was: Sharp knives and glue)


On May 12, 2006, at 10:05 AM, Berger, Daniel wrote:

>> -----Original Message-----
>> From: Logan Capaldo [mailto:logancapaldo@gmail.com]
>> Sent: Thursday, May 11, 2006 5:18 PM
>> To: ruby-talk ML
>> Subject: Re: final/closed classes in Ruby (was: Sharp knives and  
>> glue)
>
>> Unfortunately, it raises an exception way too late.
>
> Too late for whom?  Yes, you can get around it, but you have to go out
> of your way to do so.
>
> Dan
>
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I'm defining too late as 'after the damage has been done', e.g. Bar  
has already been sub-classed. I guess it comes down to a question of  
does final mean no sub-classes can be created, or no sub-classes can  
be used? If it means the first, than yes it is too late. I think that  
the distinction is especially important in Ruby because we do have  
these  #inherited style hooks, and inheriting from something can  
cause all sorts of side effects (e.g. activerecord). If someone does  
something like

class A < SomeClassFullOfDeepMagic
   final # don't want any subclasses of A
end

class B < A
end

and expects it to work, they may be in for a rude surprise, since the  
deep magic may still happen, despite the fact that an exception is  
raised.