Messaging

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Tell vs Ask

Use Tell when you don’t need a reply—logging, notifications, commands that trigger side effects. Use Ask when you need a result—queries, computations, or any flow that depends on the response.

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Message types (v4)

From v4.0.0, all message-passing APIs accept any. You can send:

• Plain Go structs (with CBOR serialization when remote)
• Protocol buffer messages (default ProtoSerializer)
• Any type registered with the serializer

The framework handles serialization when the target is on another node. Locally, messages are passed by reference without serialization.

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Message ordering

Messages between a specific sender-receiver pair are delivered in the order they were sent (FIFO). This follows from the mailbox being a FIFO queue and the single-threaded processing guarantee per actor.

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Sender context

In Receive, you can access the sender via ctx.Sender(). It returns a *PID or nil (e.g., for scheduled messages or when the sender is unknown). Use ctx.Sender().Path() when you need the sender’s address for a reply.

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ReceiveContext messaging methods

Inside Receive, the ReceiveContext provides these messaging operations: Use Sender() to get the sender’s PID when replying. Use ActorSystem().ActorOf(ctx, name) to resolve an actor by name before sending.

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No shared state

Actors never share memory. All communication is through immutable (or effectively immutable) messages. This eliminates whole classes of concurrency bugs and makes reasoning about behavior easier.