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 `false` if the input Observable emits any values, or emits `true` if the
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* input Observable completes without emitting any values.
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*
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* <span class="informal">Tells whether any values are emitted by an Observable.</span>
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*
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* 
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*
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* `isEmpty` transforms an Observable that emits values into an Observable that
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* emits a single boolean value representing whether or not any values were
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* emitted by the source Observable. As soon as the source Observable emits a
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* value, `isEmpty` will emit a `false` and complete. If the source Observable
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* completes having not emitted anything, `isEmpty` will emit a `true` and
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* complete.
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*
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* A similar effect could be achieved with {@link count}, but `isEmpty` can emit
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* a `false` value sooner.
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*
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* ## Examples
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*
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* Emit `false` for a non-empty Observable
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*
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* ```ts
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* import { Subject, isEmpty } from 'rxjs';
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*
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* const source = new Subject<string>();
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* const result = source.pipe(isEmpty());
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*
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* source.subscribe(x => console.log(x));
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* result.subscribe(x => console.log(x));
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*
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* source.next('a');
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* source.next('b');
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* source.next('c');
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* source.complete();
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*
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* // Outputs
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* // 'a'
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* // false
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* // 'b'
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* // 'c'
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* ```
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*
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* Emit `true` for an empty Observable
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*
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* ```ts
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* import { EMPTY, isEmpty } from 'rxjs';
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*
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* const result = EMPTY.pipe(isEmpty());
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* result.subscribe(x => console.log(x));
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*
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* // Outputs
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* // true
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* ```
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*
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* @see {@link count}
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* @see {@link EMPTY}
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*
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* @return A function that returns an Observable that emits boolean value
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* indicating whether the source Observable was empty or not.
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*/
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export function isEmpty<T>(): OperatorFunction<T, boolean> {
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return operate((source, subscriber) => {
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source.subscribe(
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createOperatorSubscriber(
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subscriber,
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() => {
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subscriber.next(false);
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subscriber.complete();
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},
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() => {
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subscriber.next(true);
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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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