import { Observable, Subscribable } from 'rxjs';
/**
 * Observable operator which calls the provided callbacks when observable
 * is subscribed to or unsubscribed from for the first time.
 *
 * Callbacks may be called multiple times if the last subscriber
 * is unsubscribed from it and then resubscribed again.
 *
 * @param onSubscribe - function which is called when observable
 *  is subscribed to for the first time
 * @param onUnsubscribe - function which is called when the last subscriber
 *  is unsubscribed from the observable
 */
export declare function onFirstSubscription<T>(onSubscribe: (() => void) | undefined, onUnsubscribe: (() => void) | undefined): (source: Subscribable<T>) => Observable<T>;