Phantom Agents in Scala

Phantom agents allow creating multiple distinct agent instances that share the same constructor parameters. Normally, an agent is uniquely identified by its constructor parameter values — calling get with the same parameters always returns the same agent. Phantom agents add an extra phantom ID (a UUID) to the identity, so you can have many independent instances with identical parameters.

Agent ID Format

A phantom agent's ID appends the phantom UUID in square brackets:

agent-type(param1, param2)[a09f61a8-677a-40ea-9ebe-437a0df51749]

A non-phantom agent ID has no bracket suffix:

agent-type(param1, param2)

Creating and Addressing Phantom Agents (RPC)

The Golem Scala SDK code generator produces a companion client object for each agent with these constructor methods:

Method	Description
Client.get(params...)	Get or create a non-phantom (durable) agent identified solely by its parameters
Client.newPhantom(params...)	Create a new phantom agent with a freshly generated UUID
Client.getPhantom(params..., phantom)	Get or create a phantom agent with a specific UUID

Note: Ephemeral agents only get getPhantom and newPhantom — they do not have a get method.

Example

import golem.Uuid

// Non-phantom: always the same agent for the same name
val counter = CounterClient.get("shared")

// New phantom: creates a brand new independent instance
val phantom1 = CounterClient.newPhantom("shared")
val phantom2 = CounterClient.newPhantom("shared")
// phantom1 and phantom2 are different agents, both with name="shared"

// Reconnect to an existing phantom by its UUID
val existingId: Uuid = Uuid(BigInt(42), BigInt(99))
val samePhantom = CounterClient.getPhantom("shared", existingId)

// Call methods on the phantom
phantom1.increment().map { result =>
  println(s"counter value: $result")
}

WithConfig Variants

If the agent has config fields, additional methods are generated:

• Client.getWithConfig(params..., configFields...)
• Client.newPhantomWithConfig(params..., configFields...)
• Client.getPhantomWithConfig(params..., phantom, configFields...)

Method Signature Differences

Note that in the Scala SDK, getPhantom takes the phantom UUID as the last parameter (after the constructor parameters), while newPhantom takes only the constructor parameters:

// getPhantom: constructor params first, then phantom UUID
CounterClient.getPhantom("counter-name", phantomUuid)

// newPhantom: constructor params only (UUID generated internally)
CounterClient.newPhantom("counter-name")

// newPhantom delegates to getPhantom with a generated idempotency key:
// def newPhantom(name: String): CounterRemote =
//   getPhantom(name, HostApi.generateIdempotencyKey())

Key Points

• Phantom agents are fully durable — they persist just like regular agents.
• The phantom ID is a golem.Uuid (high/low BigInt pair).
• newPhantom generates the UUID internally via HostApi.generateIdempotencyKey().
• getPhantom is idempotent: calling it with the same UUID and parameters always returns the same agent.
• Phantom and non-phantom agents with the same constructor parameters are different agents — they do not share state.
• Durable agents get get, getPhantom, and newPhantom; ephemeral agents get only getPhantom and newPhantom.