saving and loading objects

Dear all, This, I guess, would be a simple question to most of you but it is not obvious to me. I have been developing a class for a while and the most recent version of the code cannot load the objects constructed using earlier versions. What should I do in this case? How to implement a class that does not have problems of backward compatibility, especially in the presence of hidden, private and protected attributes? How to safeguard against attributes name changes, etc.? Is it a good or a bad thing to have an object whose properties could be instances of objects of a totally different class?

[Walter Roberson]

When you say "whose properties could be instances of objects of a totally different class", do you mean property in the sense of addprop() ?

[Patrick Mboma]

I do not have any experience with addprop, but I have looked it up and it looks interesting. What I meant was much simpler: you have an object of class, say, class1 and then one of its properties is an object of, say, class2.

[per isakson]

" Is it a good or a bad thing to have an object whose properties could be instances of objects of a totally different class?" It is good; it is the way to implement aggregation and composition. One cannot do without it.

"How to implement a class that does not have problems of backward compatibility" I wouldn't even try; I think that would impose too large restrictions on the design.