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import { OperatorFunction, ObservableInput, ObservedValueOf } from '../types';
import { switchMap } from './switchMap';
import { identity } from '../util/identity';
/**
* Converts a higher-order Observable into a first-order Observable
* producing values only from the most recent observable sequence
*
* <span class="informal">Flattens an Observable-of-Observables.</span>
*
* 
*
* `switchAll` subscribes to a source that is an observable of observables, also known as a
* "higher-order observable" (or `Observable<Observable<T>>`). It subscribes to the most recently
* provided "inner observable" emitted by the source, unsubscribing from any previously subscribed
* to inner observable, such that only the most recent inner observable may be subscribed to at
* any point in time. The resulting observable returned by `switchAll` will only complete if the
* source observable completes, *and* any currently subscribed to inner observable also has completed,
* if there are any.
*
* ## Examples
*
* Spawn a new interval observable for each click event, but for every new
* click, cancel the previous interval and subscribe to the new one
*
* ```ts
* import { fromEvent, tap, map, interval, switchAll } from 'rxjs';
*
* const clicks = fromEvent(document, 'click').pipe(tap(() => console.log('click')));
* const source = clicks.pipe(map(() => interval(1000)));
*
* source
* .pipe(switchAll())
* .subscribe(x => console.log(x));
*
* // Output
* // click
* // 0
* // 1
* // 2
* // 3
* // ...
* // click
* // 0
* // 1
* // 2
* // ...
* // click
* // ...
* ```
*
* @see {@link combineLatestAll}
* @see {@link concatAll}
* @see {@link exhaustAll}
* @see {@link switchMap}
* @see {@link switchMapTo}
* @see {@link mergeAll}
*
* @return A function that returns an Observable that converts a higher-order
* Observable into a first-order Observable producing values only from the most
* recent Observable sequence.
*/
export function switchAll<O extends ObservableInput<any>>(): OperatorFunction<O, ObservedValueOf<O>> {
return switchMap(identity);
}