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