Nothing stops me from implementing a Thrift or gRPC handler that uses a field from the request to look up an object in a hashmap and then call one of its method

Nothing stops me from implementing a Thrift or gRPC handler that uses a field from the request to look up an object in a hashmap and then call one of its methods with data from the request. But a distributed object system will do this implicitly on my behalf, so that the programmer’s perspective is like passing objects (by reference) over the network.