Selector semantics

Selectors are adapter-level projection functions. They do not change the underlying store state; they decide what a reactive reader receives.

React snapshots

React uses useSyncExternalStore. Its snapshot getter applies the selector and reuses the previous selection when the full store snapshot is deeply equal according to the internal deepCompare helper.

Vue, Solid, and Angular

Vue stores the latest state in a shallow ref and exposes a ComputedRef. Solid uses from plus createMemo to expose an Accessor. Angular stores a signal snapshot and returns a computed Signal.

Svelte

Svelte select creates a readable store that runs the selector for each subscription update.

Caveat

Selectors should be cheap and pure. If a selector allocates a new object every time, some adapters may still notify or recompute even when the semantic value feels unchanged.