As I understand this, the client here is not the caller of the methods defined in the interface, but the one implementing them. Caller has no problem just igno

As I understand this, the client here is not the caller of the methods defined in the interface, but the one implementing them. Caller has no problem just ignoring the methods that it doesn't need. But the implementer doesn't have that possibility. If you have a read-write interface and a read-only source, you need to resort to subpar solutions like throwing an exception.