What is a difference between `receivePartial` and `receive`?

Akka Libraries
1

I would like to understand the details between them

This topic is based on a conversation between an anonymous user of Akka and our “Ask AI about Akka” bot in the documentation.

2

In Akka, both receive and receivePartial are used to define the behavior of an actor in response to incoming messages. However, they differ in how they handle messages.

receive is a method that takes a total function as an argument. This function should cover all possible incoming messages that an actor can handle. If a message is not handled, a MatchError will be thrown at runtime. This is why it’s recommended to use a sealed trait as the super type of the commands (incoming messages) of an actor, as the compiler will emit a warning if a message type is forgotten in the pattern match. If a Behavior should not handle certain messages, you can still include them in the pattern match and return Behaviors.unhandled.

val zero: Behavior[Command] = {
  Behaviors.receiveMessage {
    case GetValue(replyTo) =>
      replyTo ! Value(0)
      Behaviors.same
    case Down =>
      Behaviors.unhandled
  }
}

(Source: Akka Docs)

On the other hand, receivePartial is a method that takes a partial function as an argument. This function only needs to cover the messages that the actor can handle. If a message is not covered by the function, it’s considered as unhandled. This can be useful to cover potential future unhandled message cases.

val zero: Behavior[Command] = {
  Behaviors.receiveMessagePartial {
    case GetValue(replyTo) =>
      replyTo ! Value(0)
      Behaviors.same
  }
}

(Source: Akka Docs)

In summary, receive requires you to handle all possible messages (or explicitly mark them as unhandled), while receivePartial allows you to only handle a subset of possible messages.