2009/11/13 Rickard Öberg <[email protected]> > On 2009-11-13 16.51, Jacek Sokulski wrote: > >> 1. Does it mean there is no (much value in) inheritance in COP? >> > > Correct, you accomplish much of the same thing using mixins.
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. > > > 2. Does it mean e.g properties one usually expect to find both in >> Manager and Employee like name, department are modelled as separate >> roles e.g. HasName, InDepartment (then the query findByName can be >> implemented for all entities with HasName role)? >> > > Correct. 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...) 2. State composition - doesn't it introduce all the problems of multiple inheritance, moreover in a hidden form? > > > 3. Is there a mechanism to restrict/define what *actual* roles an >> entity can play? Or is it the context responsibility to check if a >> Person can play the Manger role and this info should be part of >> entity/role state? >> > > The easiest way to do it is to separate between Managerable and Manager > role, so that a Manager role can only be assigned to an entity that is > Managerable. You will VERY rarely (if ever) refer to the actual entity > classes, in preferences of using the role interfaces. This makes it easier > to read the code and manage dependencies, and also makes it easier to apply > roles to various entities. > > I mean dynamic control, i.e. one Person entity may play Manger role other not (although it has potentially this ability). 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, but as the application evolves new ones will be needed. How can I add a new role to person entity without changing the existing code? Jacek
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