import type { Observable } from 'watch-state';
/**
 * React hook to subscribe a component to changes in a **watch-state** `Observable`.
 *
 * @description
 * Uses `useSyncExternalStore` for correct synchronization of external stores with React.
 * Automatically subscribes via `Watch` and unsubscribes on unmount.
 * React automatically optimizes re-renders — component only updates when the `snapshot` actually changes
 * (compared using `Object.is`).
 *
 * @example
 * ```ts
 * const $count = new State(42)
 *
 * const increase = () => {
 *   $count.value++
 * }
 *
 * const Button = () => {
 *   const num = useObservable($count)
 *
 *   return <button onClick={increase}>{num}</button>
 * }
 * ```
 *
 * @param state - **watch-state** `Observable`
 * @returns Current state value. Re-render occurs only when value actually changes.
 * @template T The type of the state value
 */
export declare function useObservable<T>(state: Observable<T>): T;