import type { Ref } from '../ref';
import type { Observer } from '../observable';
import type { Operation } from '../operation';
/**
 * Communicates the changes performed by a function on an object
 * reference to an observer.
 *
 * @param fn The function to execute
 * @param observer The observer to notify of changes
 * @returns an intrumented function
 */
export declare function observe<S, U = void>(fn: (r: Ref<S>) => U, observer: Observer<Operation<S>>): (r: Ref<S>) => U;