It’s useful to distinguish between interface and implementation dependencies. I agree that there shouldn’t be circular interface dependencies between modules. The absence of circular interface dependencies allows separate compilation of modules. It also means that at least in principle, the implementations can be made non-circular (can be refactored to non-circular without breaking any of the existing interfaces). But it’s often okay for the implementation of A to depend on the interface of B, and at the same time the implementation of B to depend on the interface of A, as long as there is no mutual dependency between the interfaces of A and B.
Comments
[The following is intended as language-agnostic.]
It’s useful to distinguish between interface and implementation dependencies. I agree that there shouldn’t be circular interface dependencies between modules. The absence of circular interface dependencies allows separate compilation of modules. It also means that at least in principle, the implementations can be made non-circular (can be refactored to non-circular without breaking any of the existing interfaces). But it’s often okay for the implementation of A to depend on the interface of B, and at the same time the implementation of B to depend on the interface of A, as long as there is no mutual dependency between the interfaces of A and B.