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