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