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import { Observable } from '../Observable';
import { SchedulerLike } from '../types';
/**
* The same Observable instance returned by any call to {@link empty} without a
* `scheduler`. It is preferrable to use this over `empty()`.
*/
export const EMPTY = new Observable<never>(subscriber => subscriber.complete());
/**
* Creates an Observable that emits no items to the Observer and immediately
* emits a complete notification.
*
* <span class="informal">Just emits 'complete', and nothing else.
* </span>
*
* 
*
* This static operator is useful for creating a simple Observable that only
* emits the complete notification. It can be used for composing with other
* Observables, such as in a {@link mergeMap}.
*
* ## Examples
* ### Emit the number 7, then complete
* ```javascript
* import { empty } from 'rxjs';
* import { startWith } from 'rxjs/operators';
*
* const result = empty().pipe(startWith(7));
* result.subscribe(x => console.log(x));
* ```
*
* ### Map and flatten only odd numbers to the sequence 'a', 'b', 'c'
* ```javascript
* import { empty, interval } from 'rxjs';
* import { mergeMap } from 'rxjs/operators';
*
* const interval$ = interval(1000);
* result = interval$.pipe(
* mergeMap(x => x % 2 === 1 ? of('a', 'b', 'c') : empty()),
* );
* result.subscribe(x => console.log(x));
*
* // Results in the following to the console:
* // x is equal to the count on the interval eg(0,1,2,3,...)
* // x will occur every 1000ms
* // if x % 2 is equal to 1 print abc
* // if x % 2 is not equal to 1 nothing will be output
* ```
*
* @see {@link Observable}
* @see {@link never}
* @see {@link of}
* @see {@link throwError}
*
* @param {SchedulerLike} [scheduler] A {@link SchedulerLike} to use for scheduling
* the emission of the complete notification.
* @return {Observable} An "empty" Observable: emits only the complete
* notification.
* @static true
* @name empty
* @owner Observable
* @deprecated Deprecated in favor of using {@link index/EMPTY} constant.
*/
export function empty(scheduler?: SchedulerLike) {
return scheduler ? emptyScheduled(scheduler) : EMPTY;
}
export function emptyScheduled(scheduler: SchedulerLike) {
return new Observable<never>(subscriber => scheduler.schedule(() => subscriber.complete()));
}
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