hunk.code_window:  * that, when applied to an item emitted by the source Observable, returns an
    * Observable.
    * @param {number} [concurrent=Number.POSITIVE_INFINITY] Maximum number of input
    * Observables being subscribed to concurrently.
    * @return {Observable} An Observable that emits the result of applying the
    * projection function (and the optional `resultSelector`) to each item emitted
    * by the source Observable and merging the results of the Observables obtained
    * from this transformation.
    * @method mergeMap
    * @owner Observable
    */
  
hunk.labels: keep keep keep keep keep replace replace replace keep keep keep
hunk.after_edit:  * projection function (and the optional deprecated `resultSelector`) to each item
    * emitted by the source Observable and merging the results of the Observables
    * obtained from this transformation.
  
hunk.file_path: src/internal/operators/mergeMap.ts
hunk.type: replace
file: import { Operator } from '../Operator';
  import { Observable } from '../Observable';
  import { Subscriber } from '../Subscriber';
  import { Subscription } from '../Subscription';
  import { OuterSubscriber } from '../OuterSubscriber';
  import { InnerSubscriber } from '../InnerSubscriber';
  import { subscribeToResult } from '../util/subscribeToResult';
  import { ObservableInput, OperatorFunction } from '../types';
  import { map } from './map';
  import { from } from '../observable/from';
  
  /* tslint:disable:max-line-length */
  export function switchMap<T, R>(project: (value: T, index: number) => ObservableInput<R>): OperatorFunction<T, R>;
  /** @deprecated resultSelector is no longer supported, use inner map instead */
  export function switchMap<T, R>(project: (value: T, index: number) => ObservableInput<R>, resultSelector: undefined): OperatorFunction<T, R>;
  /** @deprecated resultSelector is no longer supported, use inner map instead */
  export function switchMap<T, I, R>(project: (value: T, index: number) => ObservableInput<I>, resultSelector: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R): OperatorFunction<T, R>;
  /* tslint:enable:max-line-length */
  
  /**
   * Projects each source value to an Observable which is merged in the output
   * Observable, emitting values only from the most recently projected Observable.
   *
   * <span class="informal">Maps each value to an Observable, then flattens all of
   * these inner Observables.</span>
   *
   * ![](switchMap.png)
   *
   * Returns an Observable that emits items based on applying a function that you
   * supply to each item emitted by the source Observable, where that function
   * returns an (so-called "inner") Observable. Each time it observes one of these
   * inner Observables, the output Observable begins emitting the items emitted by
   * that inner Observable. When a new inner Observable is emitted, `switchMap`
   * stops emitting items from the earlier-emitted inner Observable and begins
   * emitting items from the new one. It continues to behave like this for
   * subsequent inner Observables.
   *
   * ## Example
   * Rerun an interval Observable on every click event
   * ```javascript
   * const clicks = fromEvent(document, 'click');
   * const result = clicks.pipe(switchMap((ev) => interval(1000)));
   * result.subscribe(x => console.log(x));
   * ```
   *
   * @see {@link concatMap}
   * @see {@link exhaustMap}
   * @see {@link mergeMap}
   * @see {@link switchAll}
   * @see {@link switchMapTo}
   *
   * @param {function(value: T, ?index: number): ObservableInput} project A function
   * that, when applied to an item emitted by the source Observable, returns an
   * Observable.
   * @return {Observable} An Observable that emits the result of applying the
   * projection function (and the optional `resultSelector`) to each item emitted
   * by the source Observable and taking only the values from the most recently
   * projected inner Observable.
   * @method switchMap
   * @owner Observable
   */
  export function switchMap<T, I, R>(
    project: (value: T, index: number) => ObservableInput<I>,
    resultSelector?: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R,
  ): OperatorFunction<T, I|R> {
    if (typeof resultSelector === 'function') {
      return (source: Observable<T>) => source.pipe(
        switchMap((a, i) => from(project(a, i)).pipe(
          map((b, ii) => resultSelector(a, b, i, ii))
        ))
      );
    }
    return (source: Observable<T>) => source.lift(new SwitchMapOperator(project));
  }
  
  class SwitchMapOperator<T, R> implements Operator<T, R> {
    constructor(private project: (value: T, index: number) => ObservableInput<R>) {
    }
  
    call(subscriber: Subscriber<R>, source: any): any {
      return source.subscribe(new SwitchMapSubscriber(subscriber, this.project));
    }
  }
  
  /**
   * We need this JSDoc comment for affecting ESDoc.
   * @ignore
   * @extends {Ignored}
   */
  class SwitchMapSubscriber<T, R> extends OuterSubscriber<T, R> {
    private index: number = 0;
    private innerSubscription: Subscription;
  
    constructor(destination: Subscriber<R>,
                private project: (value: T, index: number) => ObservableInput<R>) {
      super(destination);
    }
  
    protected _next(value: T) {
      let result: ObservableInput<R>;
      const index = this.index++;
      try {
        result = this.project(value, index);
      } catch (error) {
        this.destination.error(error);
        return;
      }
      this._innerSub(result, value, index);
    }
  
    private _innerSub(result: ObservableInput<R>, value: T, index: number) {
      const innerSubscription = this.innerSubscription;
      if (innerSubscription) {
        innerSubscription.unsubscribe();
      }
      this.add(this.innerSubscription = subscribeToResult(this, result, value, index));
    }
  
    protected _complete(): void {
      const {innerSubscription} = this;
      if (!innerSubscription || innerSubscription.closed) {
        super._complete();
      }
    }
  
    protected _unsubscribe() {
      this.innerSubscription = null;
    }
  
    notifyComplete(innerSub: Subscription): void {
      this.remove(innerSub);
      this.innerSubscription = null;
      if (this.isStopped) {
        super._complete();
      }
    }
  
    notifyNext(outerValue: T, innerValue: R,
               outerIndex: number, innerIndex: number,
               innerSub: InnerSubscriber<T, R>): void {
        this.destination.next(innerValue);
    }
  }
  