From: Gregory Seidman <gsslist+ruby@...>
Date: 2006-06-12T04:33:46+09:00
Subject: Re: Why the lack of mixing-in support for Class methods?

On Mon, Jun 12, 2006 at 03:48:14AM +0900, Daniel Schierbeck wrote:
[...]
} What I like about my solution is the interface -- the implementation was 
} something I just jotted down. This would of course be better (feel free 
} to point out any errors):
} 
}   class Module
}     def class_methods(&block)
}       @class_methods ||= Module.new
}       @class_methods.module_eval(&block)
}     end
} 
}     def included(mod)
}       mod.extend(@class_methods)
}     end
}   end
} 
} That way you don't need to have a constant (which clutters the namespace.)

That has two problems. First off, if you don't call class_methods before
you first include the module (e.g. you want to reopen the module later to
add class methods), the included method will fail since @class_methods is
nil. Also, including the module in another module will not behave as
expected.

See http://redcorundum.blogspot.com/2006/06/mixing-in-class-methods.html
for code and an explanation. It's similar to what you have, except:

- a little more bulletproof
- manages inclusion in modules gracefully
- requires an explicit directive to provide the
  class method mixin functionality
- provides a hook to put code in included()

} Cheers,
} Daniel
--Greg