Trait Agent 

pub trait Agent<E: Environment>: Policy<E::Observation, E::Action> {
    // Required method
    fn update(&mut self, batch: &[Experience<E::Observation, E::Action>]);
}

An agent that can act in an environment and learn from experience.

An Agent is a Policy that also knows how to update itself from batches of experience. The update logic is algorithm-specific and lives in ember-rl — this trait defines only the interface.

Separation of concerns

• Policy: pure observation → action mapping. Stateless from the caller’s perspective (though the implementation may be stateful internally).

• Agent: owns a policy and can improve it. Has mutable state.

Training loops in ember-rl work entirely in terms of Agent<E>: collect experience from E, push to a buffer, call update().

Generic over the environment

Agent<E: Environment> binds the agent to a specific environment’s observation and action types. This prevents accidentally feeding a CartPole observation to a MuJoCo agent at compile time, not runtime.

Required Methods

fn update(&mut self, batch: &[Experience<E::Observation, E::Action>])

Update the agent’s parameters from a batch of experience.

The batch may be a random sample from a replay buffer (off-policy), or a full trajectory (on-policy). The agent decides how to use it.

This is called once per training step in the outer loop.

Implementors