When is C++ covariance the best solution?

Question

This question was asked here a few hours ago and made me realise that I have never actually used covariant return types in my own code. For those not sure what covariance is

Answer 1

The canonical example is a .clone()/.copy() method. So you can always do

 obj = obj->copy();

regardless what obj's type is.

Edit: This clone method would be defined in the Object base class (as it actually is in Java). So if clone wasn't covariant, you would either have to cast, or would be restricted to methods of the root base class (which would have only very few methods, compared the class of the source object of the copy).