From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-05-13T21:47:25+09:00
Subject: Re: State Pattern Implementation

On Tue, May 13, 2003 at 08:11:38PM +0900, Robert Klemme wrote:
> > > I'd like to hear what people think: is this a reasonable
> implementation of
> > > the state pattern?
> >
> > You are representing each state by a number... with the State pattern
> > isn't each state supposed to be represented by a class ?
> 
> Normally, yes.  The association with a number is just for the ease of
> keying the example in.  My main idea was to replace the state instance by
> a redefinition of instance methods.  Pro is, you safe an instance and a
> redirection; on the con side is increased code size for the class since
> you have to include code for all states.
> 
> I'm curios to know whether anybody did this before.  I might be missing
> some grave disadvantage.

Probably stupid, but all I can think of right now:

 * easier to screw up things as the state is defined implicitly by the
   singleton methods, so you could probably reach "non-valid states" (if
   you forget to redefine one method)
 * cannot serialize these things, i.e. cannot capture the state of the
   object (related to the latter)

Finally:
 * no clean separation between the place where you define state
   transitions and the state methods/attributes (which can be a good or
   bad thing depending on how you see it)

OTOH, it is clever (extra points!!!! ;-), faster than delegation, and
uses singleton methods (we love them, don't we? :)

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