Struct Snapshot 

struct Snapshot<S> {
    alpha: f64,
    state: S,
}

The memoization snapshot backing an iterative segment.

Holds the progress already reached (alpha) and the state there. Because eval_alpha is a pure query on &self — an animation’s content is immutable once defined — the adapter keeps this snapshot behind a RefCell: advancing writes into it, projecting reads from it, and neither escapes the &self query contract. This is memoization, not mutation of the animation’s definition.

Fields

alpha: f64

state: S