Re: implementing roles in OOP......

From: Ilja Preuß (preuss_at_disy.net)
Date: 03/17/04 

Date: Wed, 17 Mar 2004 13:11:07 +0100

You might want to take a look at the Role Object pattern (do a google
search...).

Regards, Ilja

Mark Nicholls wrote:
> I am having a problem with my coding style.
>
> I have been doing OOD/A/P for several years and over those years has
> evolved to a very interface/delegation/pattern based.
>
> My problem is that basic text book implementation of 'roles' that an
> object has to satify is by implementing the interfaces of those roles.
>
> This encourages bloated classes implementing more and more interfaces
> to satisfy more and more roles and generally makes the implementation
> of that class highly coupled between internal states and role.
>
> There is no context for the role i.e. so if I have an object which is
> both a a member of two hierachies in two different contexts there is a
> interface clash
> e.g. a person is a member of a network of family members and a member
> of network of work colleagues so....
>
> class CPerson : IFamilyNode,IEmployeeNode
> {
> bla bla bla
> }
>
> but really I want to use a generic node implementation class in two
> different roles here, the fact that I have two different contexts
> shouldn't really be a problem.
>
> but I can't go
>
> class CPerson : INode,INode // interfaces clash
> {
>
> }
>
> I can ask the object for a reference to an interface to that role (and
> it's completely up to the class how it implements that interface i.e.
> by itself, by returning a contained object, by creating a new role
> implementer.....).
>
> This gives a very different style of programming and a whole host of
> questions.
>
> i.e. something like
> class CPerson
> {
> INode AsFamilyNode()
> {
> hmmm now how shall I implement this role?
> }
>
> INode AsEmployeeNode()
> {
> hmmm now how shall I implement this role?
> }
> }
>
> Is there any standard books/literature that discuss this style of
> coding?
>
> There are all sorts of questions about identity, what is a role and
> what is a class, should roles be able to have sub roles, should I be
> able to add and remove roles, how should I process composite
> structures of these roles, how can I create reusable role
> implementation and compose them together etc etc etc.....
>
> I've sort of looked at web sites for "Role based modelling" and
> similar subjects but they are thin on implementation - sticking to the
> relative sterile simplicity of the modelling rather than the dirt and
> mess of the real world implementation.

Relevant Pages

  • Re: Design Problem Aggregation
    ... >Class E has a member of type A. ... As D is the base class of E and F we can add to the container ... >that interface in E and F. A and B have many member functions and I ... This is called the Interface Segregation Principle. ...
    (comp.object)
  • Re: abstract class does not implement interface member ...
    ... saying that a protected member can not expose an internal ... Why can't I return an internal interface from a protected member ... internal interface IInvocableInternals: IInvocable ...
    (microsoft.public.dotnet.languages.csharp)
  • Re: Expose members of contained class
    ... you would still need to write some sort of custom binder that uses a custom mechanism in your type to retrieve the implementation interface for the type. ... It's possible you can customize what it generates; I think VS uses the "snippets" feature to do that work, so I suppose you could replace the stock "snippet" " statements with one that calls some default instance member. ...
    (microsoft.public.dotnet.languages.csharp)
  • Recomendation for Public Safety Use
    ... I am a member of a volunteer ambulance service and am looking for a good GPS receiver for my service's use. ... -Vehicle mounted with external antenna and hardwired power supply, but can be removed with minimal fuss and used portable with built-in antenna and battery supply. ... -Computer interface with standard communication protocol. ...
    (sci.geo.satellite-nav)
  • Re: [KVM PATCH v2 2/2] kvm: add support for irqfd via eventfd-notification interface
    ... So what is your proposal for such interface? ... Alternatively, a new fileop ->signal_event, which would map to ... irq contexts. ... and make eventfd and irqfd the first implementations. ...
    (Linux-Kernel)