import { Observable } from '../Observable';
import { SchedulerLike } from '../types';
/**
 * Creates an Observable that emits sequential numbers every specified
 * interval of time, on a specified IScheduler.
 *
 * <span class="informal">Emits incremental numbers periodically in time.
 * </span>
 *
 * <img src="./img/interval.png" width="100%">
 *
 * `interval` returns an Observable that emits an infinite sequence of
 * ascending integers, with a constant interval of time of your choosing
 * between those emissions. The first emission is not sent immediately, but
 * only after the first period has passed. By default, this operator uses the
 * `async` IScheduler to provide a notion of time, but you may pass any
 * IScheduler to it.
 *
 * @example <caption>Emits ascending numbers, one every second (1000ms)</caption>
 * var numbers = Rx.Observable.interval(1000);
 * numbers.subscribe(x => console.log(x));
 *
 * @see {@link timer}
 * @see {@link delay}
 *
 * @param {number} [period=0] The interval size in milliseconds (by default)
 * or the time unit determined by the scheduler's clock.
 * @param {Scheduler} [scheduler=async] The IScheduler to use for scheduling
 * the emission of values, and providing a notion of "time".
 * @return {Observable} An Observable that emits a sequential number each time
 * interval.
 * @static true
 * @name interval
 * @owner Observable
 */
export declare function interval(period?: number, scheduler?: SchedulerLike): Observable<number>;