Preserve Run-Time Class - What should I expect when casting a parent to a child?

[Mark Smith]

I'm using the preserve run time class function to cast an incoming object like this.

When I pass a parent class object into the EventMessage in, the current value of the parent class property is not preserved on the output. When I pass in a child class, the parent property is preserved. It's like a new default instance of the child class is created when I pass in the parent rather than a child class instance that has the incoming parent's properties preserved and defaults for the undefined child class properties. I expected the preserve run time class function to take the instance of the parent and "deep-copy" it a new child instance if the parent was on the wire. Apparently, I'm wrong about that. But I have to ask why this behavior? I can't think of why one wouldn't want to preserve the parent's properties as part of a cast (it seems that's a safe cast, like casting a 16 bit int to a 32). What am I missing?

Thanks,

Mark

[Yair]

The PRTC primitive does not cast a parent to a child. It takes an existing child which is traveling on a parent wire and outputs it as a child wire. If the data in the left input is NOT a child, the primitive should return an error (and, as you've seen, a default child).

[Mark Smith]

Yair,

Thanks for the info - so I'm expecting more from the function that it's designed to do - I guess the function name explains it if I read carefully . Still, would it be useful to have a function that could convert (actually deep copy) a parent to a child and preserve the parent's data since it seems that would always be a safe thing to do? As far as I can tell, the To More Specific class VI would do the same thing as the Preserve Run Time Class - that is, fail and return a default instance of the child.

Thanks,

Mark

[ned]

This has been asked before; there's no way to take a parent class and turn it into a child containing the same parent data as the input. See for example here: http://lavag.org/topic/13383-how-to-properly-cast-object-to-child-class/

[Mark Smith]

This has been asked before; there's no way to take a parent class and turn it into a child containing the same parent data as the input. See for example here: http://lavag.org/top...to-child-class/

I must be getting old... I participated in that thread so I should have remembered all this.

Thanks,

Mark