import { OperatorFunction } from '../types';
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import { operate } from '../util/lift';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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/**
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* Emits a given value if the source Observable completes without emitting any
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* `next` value, otherwise mirrors the source Observable.
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*
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* <span class="informal">If the source Observable turns out to be empty, then
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* this operator will emit a default value.</span>
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*
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* 
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*
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* `defaultIfEmpty` emits the values emitted by the source Observable or a
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* specified default value if the source Observable is empty (completes without
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* having emitted any `next` value).
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*
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* ## Example
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*
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* If no clicks happen in 5 seconds, then emit 'no clicks'
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*
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* ```ts
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* import { fromEvent, takeUntil, interval, defaultIfEmpty } from 'rxjs';
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*
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* const clicks = fromEvent(document, 'click');
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* const clicksBeforeFive = clicks.pipe(takeUntil(interval(5000)));
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* const result = clicksBeforeFive.pipe(defaultIfEmpty('no clicks'));
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* result.subscribe(x => console.log(x));
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* ```
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*
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* @see {@link empty}
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* @see {@link last}
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*
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* @param defaultValue The default value used if the source
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* Observable is empty.
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* @return A function that returns an Observable that emits either the
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* specified `defaultValue` if the source Observable emits no items, or the
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* values emitted by the source Observable.
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*/
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export function defaultIfEmpty<T, R>(defaultValue: R): OperatorFunction<T, T | R> {
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return operate((source, subscriber) => {
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let hasValue = false;
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source.subscribe(
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createOperatorSubscriber(
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subscriber,
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(value) => {
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hasValue = true;
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subscriber.next(value);
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},
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() => {
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if (!hasValue) {
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subscriber.next(defaultValue!);
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}
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subscriber.complete();
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}
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)
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);
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});
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}
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