[lp251]

You can, but sometimes it’s not ideal.

I ran into this when A and B had many derived classes. I wanted to put A and it’s derived classes in one module, and B and it’s derived classes in another. It was messy.

I wound up putting A and B in a single module and having a separate one for the derived classes. Not ideal.

[nemetroid]

It does sound ideal to me, or at least better than the initial proposal.

A and B both need to know about the other's base definition, neither cares about the details about the other's derived classes. Splitting it into three modules shares as little surface area as possible.