In reply to bmorris:
Thanks Morris.
I have one point to add.
The assignment from child_handle to parent_handle is always allowed, but an assignment the reverse direction can only be checked at runtime using $cast.
In the simulation you had pointed me to, I notice that the last D0.display() after casting ($cast(D0,C0)) prints “D!” in output console. $cast(D0, C0) doesn’t throw errors only because, we assign C0 = D0 before casting. Had we not done C0 = D0, this would have been an error.
Error-[DCF] Dynamic cast failed
testbench.sv, 57
Casting of source class type ‘C’ to destination class type ‘D’ failed due to
type mismatch.
Please ensure matching types for dynamic cast