I am trying to figure out the dynamic-cast and dynamic-new. I have written a class that my programmers will use normally, but I want them to be able to change the the class that is used if they need to. I also want them to be able to access any methods in the sub-class they define. Basically here is what I have right now.
DEFINE VARIABLE customClass AS sms.lib.customClass NO-UNDO.
DEFINE VARIABLE cName AS CHARACTER NO-UNDO.
update cName.
customClass = DYNAMIC-NEW cName ( ).
Now using that I can access the class and the methods in the super class, but I can not access the methods defined in the sub class. Now I know that I need to use the dynamic-cast, but I am just getting used to OO Programming and the documentation is not very clear to me. Can anyone give me pointers on how to do this?
Message was edited by:
Frederic Boisseau
You actually do not need to use dynamic cast if you know the subclass type which I assume you do if you are writing specific code to access the subclass specific methods. Just downcast the super class object reference and you have an instance of the subclass (which of course you had all along - just not access to the subclass members.
-Shelley
That is the issue, I will not know the subclass, I will just know the superclass (if I have the terms correct). The programmer will be able to specify the specific subclass they will use, which will be based on the superclass that I have previously defined. Using the example that I posted, the superclass is sms.lib.customClass. I know that all the subclasses defined will be of that type, but can have other methods added to them.
So let assume that a programmer has written sms.lib.specialClass which is of the type sms.lib.customClass. In sms.lib.customClass, I have written a method called 'sayHello', and the programmer added to sms.lib.specialClass a method called 'sayGoodbye'. Now I can reference 'sayHello' using the DYNAMIC-NEW, but I can not reference 'sayGoodbye'.
How do I access 'sayGoodbye'?
How do you know there is a sayGoodbye method to reference if you don't know the object is of type sms.lib.specialClass?
To be able to call sayGoodbye you need to be sure it's there.
There are only 3 ways to know:
The sayGoodbye method is defined in customClass (it can still be overwritten in specialClass)
sayGoodbye is defined in an interface implemented by specialClass (in that case cast the object to the interface type and call it from there)
sayGoodbye is only defined in specialClass (in that case you know the object should be of type specialClass if you want to call it.)
I vote for the Interface.
Another opotion might be to create a "Dispatch" method in the super class and override that in the custom class. This Dispatch method would receive a parameter for the method name and execute that method. It get's a bit tricky if there are paramters involved - But that's probably doable.
Never the less: Use Interfaces.
+1 for interfaces.