actortype

Actortype is a term used in actor-based programming to describe the classification of an actor by its behavior and message protocol. An actortype encapsulates the set of messages that an actor can receive, the kinds of state changes it can perform, and the ways it can respond to or forward messages. By defining actortypes, systems can express actor interfaces independently from their concrete implementations, enabling safer composition and easier testing.

In practice, an actortype is realized through a type-level or protocol-level description of an actor’s behavior. Some frameworks expose a typed behavior or protocol that governs how an actor of that type handles messages. For example, in typed actor systems like Akka Typed, the behavior describes the allowed messages and the corresponding handling logic; in Erlang/OTP, the behavior of a process is described by its API, such as gen_server or supervisor specifications. Actortypes can support supervision, routing, and fault tolerance by allowing the runtime to inspect the expected message set and to validate interactions.

Benefits of using actortypes include clearer contracts between components, better testability via mock actors, and potential tooling support for documentation, client generation, and protocol evolution. They also aid in evolution and versioning of interfaces, since changes to an actortype can be detected and managed at design time or runtime.

Limitations include the dynamic nature of message patterns in some systems, where protocols evolve, and the fact that actortype terminology is not universally standardized across frameworks. See also: actor model, typed actors, protocol, supervision, Akka.