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From Daniel Fagerstrom <dani...@nada.kth.se>
Subject Re: [RT] Bidirectional relationships for blocks?
Date Wed, 30 Mar 2005 10:57:58 GMT
Carsten Ziegeler wrote:

>I might be wrong but I think up to now we only talked about one block
>depending on another block and this is then a one-way relationship.
>
>But what if we need a bidirectional relationship? I have currently two
>examples:
>a) Skins
>We briefly talked about one use-case for blocks: skins. You factor out
>the layout of your application into a skin block and then can simply
>switch to a different block implementing the skin contract. Now, what if
>the skin block needs some information from the "application block" like
>some user settings or whatever?
>
>b) Plugins or portlets
>I could imagine to bundle portles for the cocoon portal engine as simple
>blocks conforming to a cocoon portlet contract. So the portal block uses
>the portlet blocks, but in addition a portlet block needs access to some
>portal services.
>The same would apply if you would use the block concept to implement
>some kind of plugins.
>
>Does this make sense? Or is this FS?
>  
>
The kind of polymorphism I have been talking about atacks exactly the 
scenarios you describe. And from having used it in a number of 
applications that I have been involved in developing during the last 
year I can tell that it is a really convinient to reuse and extend e.g. 
skins, in this way. There might be other design patterns for this, but I 
have not seen any as smooth yet.

/Daniel


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