Reference Target

The Reference Target semantic module constrains an entity reference to a specific entity type. A targeted ref links one entity to another entity of a declared type. Here, the task’s started event records which Worker runs it.

YAML model

quent: alpha
model: references

entities:
  Worker:
    events:
      registered: {}

  Task:
    events:
      started:
        attributes:
          worker: { ref: Worker }
      ended: {}

Instrumentation API

An entity handle produces a typed reference with as_entity_ref. The generated started method only accepts a reference targeting Worker.

// 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"), "/references.rs"));
}

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

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

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

    let mut task = context.observer::<Task>().handle();
    // A `Task` reference has the wrong target type, so this would not compile:
    // let other_task = context.observer::<Task>().handle();
    // task.started(other_task.as_entity_ref())?;
    task.started(worker.as_entity_ref())?;
    task.ended()?;

    Ok(())
}