Struct SeededRng 

pub struct SeededRng { /* private fields */ }

A deterministic, snapshot/restore-able RNG for record-and-replay.

Backed by rand_chacha::ChaCha20Rng. Given the same seed and the same number of draws, every instance produces the identical u64 sequence; snapshot + restore reproduces the remaining draws exactly, and split yields an independent substream that does not perturb the parent.

Implementations

impl SeededRng

pub fn from_seed(seed: u64) -> Self

Construct from a 64-bit seed. The full 256-bit ChaCha key is derived by zero-extending the seed (this is ChaCha20Rng::seed_from_u64).

pub fn next_u64(&mut self) -> u64

Draw the next u64 from the stream, advancing position.

pub fn snapshot(&self) -> RngState

Capture the current position so it can be restored later to reproduce the identical subsequent draw sequence.

pub fn restore(state: RngState) -> Self

Rebuild a SeededRng positioned exactly where state was taken.

pub fn split(&mut self) -> Self

Fork an independent substream. The child shares the seed but selects a distinct ChaCha stream, so its draws never overlap the parent’s and splitting does not consume any of the parent’s keystream.