Entity references

An attribute of type ref identifies another entity instance by its UUID. The reference is type-erased: the generated API knows that it is an entity reference, but does not restrict which entity type it targets. This is useful when any kind of entity is a valid target.

YAML model

quent: alpha
model: untyped_references

entities:
  Worker:
    events:
      started: {}
      ended: {}

  Task:
    events:
      started:
        attributes:
          source: ref
      ended: {}

Instrumentation API

Every entity handle can produce a type-erased reference. Here, as_any_entity_ref produces a reference to the Worker instance for the task’s started event.

// SPDX-FileCopyrightText: Copyright (c) 2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0

#[allow(unused)]
mod instrumentation {
    include!(concat!(env!("OUT_DIR"), "/untyped_references.rs"));
}

use instrumentation::{Context, Noop, Task, UntypedReferences, Worker};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let context = Context::<UntypedReferences>::try_new(Noop)?;

    let mut worker = context.observer::<Worker>().handle();
    worker.started()?;

    let mut task = context.observer::<Task>().handle();
    task.started(worker.as_any_entity_ref())?;
    task.ended()?;

    worker.ended()?;

    Ok(())
}

When an attribute must target a particular entity type, the Reference Target semantic module adds that restriction to the generated API.