> how can a message be 'lost' from a mailbox without any explicit 'read-message-from-mailbox' call from the actor itself.
It depends on the implementation of actors. If an actor is represented as a thread/fiber then an actor is responsible to call `receive` method from time to time. The only example of such an approach I know in the C++ world is Just::Thread Pro library. But even in that case, a message can be ignored if a user writes the wrong if-then chain (or `switch` statement).
But actors often implemented as an object with callbacks those are called by actor framework at the appropriate time. List of callbacks can differ from state to state.
It depends on the implementation of actors. If an actor is represented as a thread/fiber then an actor is responsible to call `receive` method from time to time. The only example of such an approach I know in the C++ world is Just::Thread Pro library. But even in that case, a message can be ignored if a user writes the wrong if-then chain (or `switch` statement).
But actors often implemented as an object with callbacks those are called by actor framework at the appropriate time. List of callbacks can differ from state to state.