I have a set of concrete classes which all inherit from an abstract class. The client code which references them only knows them as instances of the abstract class (I have a parameterised constructor method, which is working fine).
The instances all contain elements which can contain primitive types or else contain other elements. This follows the Composite design pattern. The instances hide all details of these elements from the client code. The client code needs make a deep copy of an instance, which will involve copying all the elements and their child elements, even though the client doesn't know about these. (Ultimately, it also will also need to 'add' two instances together to form a third instance, which will involve 'adding' all the child elements together, but this would follow the same principle as the deep copy). To achieve this, I though it would be straightforward to pass the instance to be copied to a class method in the abstract class. This would determine the actual class and create a new instance of that class. It should then be possible to pass the new instance to a method in the passed instance. This method would copy its child elements, and tell each of its children to do the same. These copy methods could all be protected methods of the abstract classes, meaning they would be visible to the cloning class method and the instances themselves, but not to the client code, which would only need to call the public cloning class method. I started to write it, as the code example below. Although the class type is correctly detected, and the object is apparently created, the constructors the abstract class or the concrete class are not called. I have code in both of these, and both are being called if I create the object in the client code using the parameterised constructor method, or 'normally' using TConcreteClass.Create. What am I doing wrong? Thanks, Robin ------------------------ interface class function Clone(ConcreteInstance: TAbstractClass): TAbstractClass; implementation class function TAbstractClass.Clone(ConcreteInstance: TAbstractClass): TAbstractClass; var ConcreteClass: TClass; begin //Determine class of passed object ConcreteClass := ConcreteInstance.ClassType; //Create a new object of the appropriate class - //WHY are NEITHER constructors of concrete class //NOR abstract class being called?! Result := ConcreteClass.Create as TAbstractClass; //Tell passed object to deep copy its attributes to the //newly created object, which will tell its children //to do the same, and so on ConcreteInstance.DeepCopy(Result); end; ----------------------------------------------------- Home page: http://groups.yahoo.com/group/delphi-en/ To unsubscribe: [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/delphi-en/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
