import { Observer } from '../Observer';
import { Observable } from '../Observable';
/**
 * Returns a mirrored Observable of the source Observable, but modified so that the provided Observer is called
 * for every item emitted by the source.
 * This operator is useful for debugging your observables for the correct values or performing other side effects.
 * @param {Observer|function} [nextOrObserver] a normal observer callback or callback for onNext.
 * @param {function} [error] callback for errors in the source.
 * @param {function} [complete] callback for the completion of the source.
 * @reurns {Observable} a mirrored Observable with the specified Observer or callback attached for each item.
 */
export declare function _do<T>(nextOrObserver?: Observer<T> | ((x: T) => void), error?: (e: any) => void, complete?: () => void): Observable<T>;