On Mon, Nov 16, 2009 at 5:48 PM, Jacek Sokulski <[email protected]> wrote:
> Have you tried to implement basic patterns in COP? It should be a good test > for COP expressiveness, as patterns are usually compensation for language > shortcomings. You give me the pattern, and I will take a shot at a replacement. > There are two possible reservations: > 1. The logic of an entity is scattered in many places. From an interaction > point of view it is can be an advantage, since the entity participates in > interaction through one of its roles, but understanding the whole behaviour > of an entity can be difficult (even in the case of one role, the role can > require other roles that require still other roles...) Potentially true, but also a good way to measure decoupling/cohesion balance... > 2. State composition - doesn't it introduce all the problems of multiple > inheritance, moreover in a hidden form? Nope. Since methods are resolved one-by-one, there is always an easily predictable resolution of a method's constituents. In multiple-inheritance languages, such as C++, the resolution must be at class level, and no easily understood resolution algorithm. > I mean dynamic control, i.e. one Person entity may play Manger role other > not (although it has potentially this ability). There are several ways to implement this. For instance, an entity that is created as a Employee can be retrieved later as a Manager. >Another point is dynamic > roles composition: a person can play possible hundreds of roles, but from > the application point of view only several are interesting, "hundreds of roles" is probably not feasible in any real application. Show me with an example of what you are trying to say... > How can I add a new role to > person entity without changing the existing code? I think you see this as a problem because of OOP conditioning. Types are not related to the serialized state. You don't need to "add a role" to an entity, since the roles are not stored. Instead, you effectively do; "Ok, here is a Role (an interface) and load up Entity 1234 into that role." There are some nastiness hidden in the fine details, for instance that potentially the different roles could be stored in different entity stores, and therefor the retrieval of the old state would fail, and entity stores that needs type mapping can't be used and possibly others. But in general, this is fairly straight-forward. Cheers -- Niclas Hedhman, Software Developer http://www.qi4j.org - New Energy for Java I live here; http://tinyurl.com/2qq9er I work here; http://tinyurl.com/2ymelc I relax here; http://tinyurl.com/2cgsug _______________________________________________ qi4j-dev mailing list [email protected] http://lists.ops4j.org/mailman/listinfo/qi4j-dev
