Type Alias Snapshot 

pub type Snapshot = Arc<HashMap<MeasureId, Arc<MeasureValues>>>;

Every tracked derived measure’s values after an edit round.

Copy-on-write: cloning a Snapshot is a reference-count bump, and the engine shares unchanged measures between successive snapshots. An edit round copies the outer map (one Arc per measure) and only the measures whose cells changed, and only if a caller still holds the previous snapshot; drop the old one first and an edit costs just its delta.

Aliased Type

pub struct Snapshot { /* private fields */ }