Design Patterns discussion

[Lorenzo Bettini <bettini AT dsi.unifi.it>]

rajesh AT cs.iitm.ernet.in
 wrote:
> Dear members,
>
> What is main difference between Decorator and Visitor pattern? I can not 
> find any difference? Both are used to add additional responsibilities 
> dynamically. why one is categorized into structural and other in behaviorial categories? 
> I wonder if some body could clarify my doubt. Looking forward for reply.

well Decorator lets you create a "chain" of objects (each object is 
inside the other) and each object "specializes" a behavior (i.e. it 
performs the behavior of the included object and performs its own 
behavior), w.t.r. it is structural.

Visitor lets you act differently according the dynamic type of objects 
(a sort of manual implementation of double dispatch, see, e.g., 
http://www.lorenzobettini.it/software/doublecpp), and w.t.r. it is 
behavioral...

Hope it helps

Lorenzo

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