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import { Observable } from '../Observable';
import { MonoTypeOperatorFunction } from '../types';
/**
* Emits the most recently emitted value from the source Observable whenever
* another Observable, the `notifier`, emits.
*
* <span class="informal">It's like {@link sampleTime}, but samples whenever
* the `notifier` Observable emits something.</span>
*
* ![](sample.png)
*
* Whenever the `notifier` Observable emits a value or completes, `sample`
* looks at the source Observable and emits whichever value it has most recently
* emitted since the previous sampling, unless the source has not emitted
* anything since the previous sampling. The `notifier` is subscribed to as soon
* as the output Observable is subscribed.
*
* ## Example
* On every click, sample the most recent "seconds" timer
* ```ts
* import { fromEvent, interval } from 'rxjs';
* import { sample } from 'rxjs/operators';
*
* const seconds = interval(1000);
* const clicks = fromEvent(document, 'click');
* const result = seconds.pipe(sample(clicks));
* result.subscribe(x => console.log(x));
* ```
*
* @see {@link audit}
* @see {@link debounce}
* @see {@link sampleTime}
* @see {@link throttle}
*
* @param {Observable<any>} notifier The Observable to use for sampling the
* source Observable.
* @return {Observable<T>} An Observable that emits the results of sampling the
* values emitted by the source Observable whenever the notifier Observable
* emits value or completes.
* @method sample
* @owner Observable
*/
export declare function sample<T>(notifier: Observable<any>): MonoTypeOperatorFunction<T>;