Trait ReplayBuffer 

pub trait ReplayBuffer<O, A>
where
    O: Clone + Send + Sync,
    A: Clone + Send + Sync,
{
    // Required methods
    fn push(&mut self, experience: Experience<O, A>);
    fn sample(
        &self,
        batch_size: usize,
        rng: &mut impl Rng,
    ) -> Vec<Experience<O, A>>;
    fn len(&self) -> usize;
    fn capacity(&self) -> Option<usize>;

    // Provided methods
    fn is_empty(&self) -> bool { ... }
    fn is_full(&self) -> bool { ... }
    fn ready_for(&self, batch_size: usize) -> bool { ... }
}

A buffer that stores past experience for agent training.

Used primarily by off-policy algorithms (DQN, SAC, TD3) to break temporal correlations between training samples. On-policy algorithms (PPO, A2C) typically collect fixed-length trajectories instead and don’t need this trait — they can use a plain Vec<Experience<O, A>>.

Implementing this trait

The most common implementation is a circular buffer with a fixed capacity that overwrites the oldest experience when full. Concrete implementations live in ember-rl, not here.

Bounds

O: Clone + Send + Sync and A: Clone + Send + Sync are required because sampling returns owned Experience values (not references), and buffers may be accessed across threads during async training.

Required Methods

fn push(&mut self, experience: Experience<O, A>)

Add a new experience to the buffer.

If the buffer is at capacity, implementations should overwrite the oldest experience (FIFO eviction).

fn sample(&self, batch_size: usize, rng: &mut impl Rng) -> Vec<Experience<O, A>>

Sample a random batch of batch_size experiences.

Sampling is done with replacement. The caller supplies the RNG so sampling randomness can be seeded and controlled independently.

Panics

Implementations may panic if batch_size > self.len().

fn len(&self) -> usize

The number of experiences currently stored.

fn capacity(&self) -> Option<usize>

The maximum number of experiences the buffer can hold, if bounded.

Returns None for unbounded buffers (e.g. trajectory collectors).

Provided Methods

fn is_empty(&self) -> bool

Returns true if the buffer contains no experiences.

fn is_full(&self) -> bool

Returns true if the buffer is at capacity.

When full, the next push() will overwrite the oldest experience.

fn ready_for(&self, batch_size: usize) -> bool

Returns true if the buffer has enough experience to sample a batch of the given size.

Useful for deciding when to start training in the warm-up phase.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors