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Events

Events are log entries emitted during execution. They're useful for tracking actions and state changes.

Defining Events​

Use the event keyword to define an event structure:

event TransferEvent:
    topic from Identifier
    topic to Identifier
    field amount U64
    field timestamp U64
Limits
  • Up to 4 topics per event
  • Up to 256 fields per event
  • Only primitive types allowed

Emitting Events​

Direct Emit​

emit TransferEvent{
    from: sender_id,
    to: recipient_id,
    amount: 100,
    timestamp: now
}

Emit to Actor Context​

By default, events log to the logic context. Use -> to log to an actor's context:

emit TransferEvent{...} -> Sender     // Log to sender's context
emit TransferEvent{...} -> recipient  // Log to specific actor

Classes with Events​

Classes can implement __event__ to be emitted directly:

class Registration:
    field name String
    field counter U64

    method __event__() -> (ev RegistrationEvent):
        ev = RegistrationEvent{
            user_name: self.name,
            count: self.counter
        }

event RegistrationEvent:
    topic user_name String
    field count U64

Then emit the class directly:

memory reg = Registration{name: "Alice", counter: 1}
emit reg -> Sender  // Calls __event__ automatically

String Emits and builtin.Log​

When you emit a string or f-string, Coco generates a builtin.Log event:

emit "Simple log message"
emit f"Transferred {amount} tokens"

These builtin.Log events appear in event queries and can be used for debugging and audit trails.

Complete Example​

coco Logger

event UserAction:
    topic user Identifier
    topic action String
    field details String

endpoint dynamic LogAction(action String, details String):
    emit UserAction{
        user: Sender,
        action: action,
        details: details
    }

    // Or emit to sender's context
    emit UserAction{
        user: Sender,
        action: action,
        details: details
    } -> Sender