Trait Policy

Source

pub trait Policy {
    type Reading;
    type Command;

    // Required method
    fn evaluate(&mut self, reading: &Self::Reading) -> Reaction<Self::Command>;
}

Expand description

The decision half of a node: what one reading calls for.

A Controller is the policy behind every built-in kind, deciding an f32 reading into an on/off command. A policy of your own decides whatever a driver reads, a whole measurement struct included, into whatever an actuator takes, and Node::with_policy runs it in the same read, decide, act, publish loop. Evaluation is synchronous and hardware-free, so a policy is unit-testable with no devices and no network.

§Examples

use pamoja_profile::{Alert, Policy, Reaction};

// Frost settles when the air is cold and damp, so this reads both at once and
// switches a heater, raising its own condition when the risk is on.
struct FrostGuard {
    warn_below: f32,
}

impl Policy for FrostGuard {
    type Reading = (f32, f32);
    type Command = bool;

    fn evaluate(&mut self, &(temperature, humidity): &(f32, f32)) -> Reaction {
        let risk = temperature < self.warn_below && humidity > 80.0;
        Reaction {
            actuator: Some(risk),
            alert: risk.then_some(Alert::Custom { code: "FrostRisk", value: temperature }),
        }
    }
}

let mut guard = FrostGuard { warn_below: 2.0 };
let cold = guard.evaluate(&(1.0, 92.0));
assert_eq!(cold.actuator, Some(true));
assert_eq!(cold.alert.map(Alert::kind), Some("FrostRisk"));
assert_eq!(guard.evaluate(&(1.0, 40.0)).alert, None);