import { OperatorFunction } from '../types';
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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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* ```javascript
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* import { Subject } from 'rxjs';
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* import { isEmpty } from 'rxjs/operators';
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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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* source.subscribe(x => console.log(x));
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* result.subscribe(x => console.log(x));
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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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* // Results in:
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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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* ```javascript
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* import { EMPTY } from 'rxjs';
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* import { isEmpty } from 'rxjs/operators';
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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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* // Results in:
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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 {OperatorFunction<T, boolean>} An Observable of a boolean value indicating whether observable was empty or not
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* @method isEmpty
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* @owner Observable
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*/
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export declare function isEmpty<T>(): OperatorFunction<T, boolean>;
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