From: gwtmp01@...
Date: 2005-12-02T07:49:10+09:00
Subject: Re: abstract class


On Dec 1, 2005, at 3:12 PM, Trans wrote:
> What do you use this for?

Sometimes you have an abstract class that models all the common  
behavior but
to "complete" the functionality some methods need to be defined/ 
overridden
in the subclasses.  In this situation, instantiating the abstract  
class is
an error since it is only the subclasses that are "complete".  I just  
had
a use for this pattern and I decided to just make #new private:

	class Base
	  class <<self; private :new; end
         end

	class Derived < Base
	  class <<self; public :new; end
         end

The advantage to this is you can still have common initialization  
code in
Base#initialize but it can only be accessed by calling super from
#initialize in a subclass.

It is similar to how Enumerable doesn't make sense as a class because
it isn't complete without #each being defined.