import { Observable } from 'rxjs';
/**
 * Example:
 * import {from} from 'rxjs/observable/from';
 * from([1, 2, 3])
 * 	.pipe(doOnSubscribe(() => console.log('subscribed to stream')))
 * 	.subscribe(x => console.log(x), null, () => console.log('completed'));
 */
export declare function doOnSubscribe<T>(onSubscribe: () => void): (source: Observable<T>) => Observable<T>;