On Sat, 2012-02-11 at 18:06 +1030, Bruce Bruen wrote: > On Fri, 2012-02-10 at 21:59 -0300, Fabián Flores Vadell wrote: > > 2012/2/10 Emil Lenngren <emil.lenng...@gmail.com> > > > <etc> > > Interesting, I have a similar problem, perhaps the same but maybe > slightly different. > > I have a base class that is CREATE PRIVATE, it cannot be instantiated > directly by a client application. It contains various methods that must > be available to it's child classes (which CAN be instantiated) and can > be called by the client application. For example, DBAdd is public in > the base class so that the child class can call it. > > What I have done, with some success is as follows: > > In the base class I inspect the System.Backtrace and compare the object > indicated by the second item (i.e. System.Backtrace[1]) to see that it > "IS" a Me. (is that clear, if not I'll have to go find the code?) > IOW I check that the caller object is an instance of Me, which can only > be the base class itself or a class that inherits the base class. If > not, I just raise an "Illegal Call" error. > > This works within reason, however it has the following drawbacks: > a) there is obviously an overhead involved in the check code > b) it does not prevent a client application from instantiating an object > that inherits directly from the base class. > So it goes. > > To expand this further. I also have examples where I need (read "want") > to have methods in the base class that MUST be overridden in the > specialised child classes. This is because these methods are templates > only. However, they must be present in the base class, as the base class > calls these methods! IOW the base class calls "SomeMethod", which my > design says "must be implemented in the child class". Gambas is > (almost) great at achieving this by its' use of virtual dispatch. If the > child class has correctly overridden the base class method, then that is > the one that is called. And in the base class, I can have a "stub" > method that simply raises an error. If the child class does not > override the method the the error is raised. > > I would love to be able to solve problem b) above. > Oh, by the way, the only way I can think of solving b) is to exchange some sort of signature when the objects are created. However, I don't think this can work as the base class is instantiated first by gambas. B
------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Gambas-user mailing list Gambas-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/gambas-user
