fix(mergeAll): use higher-order lettable version of mergeAll

src/operator/mergeAll.ts

@@ -1,10 +1,6 @@
 import { Observable } from '../Observable';
-import { Operator } from '../Operator';
-import { Observer } from '../Observer';
-import { Subscription } from '../Subscription';
-import { OuterSubscriber } from '../OuterSubscriber';
 import { Subscribable } from '../Observable';
-import { subscribeToResult } from '../util/subscribeToResult';
+import { mergeAll as higherOrder } from '../operators/mergeAll';
 
 export function mergeAll<T>(this: Observable<T>, concurrent?: number): T;
 export function mergeAll<T, R>(this: Observable<T>, concurrent?: number): Subscribable<R>;
@@ -54,56 +50,5 @@ export function mergeAll<T, R>(this: Observable<T>, concurrent?: number): Subscr
  * @owner Observable
  */
 export function mergeAll<T>(this: Observable<T>, concurrent: number = Number.POSITIVE_INFINITY): T {
-  return <any>this.lift<any>(new MergeAllOperator<T>(concurrent));
-}
-
-export class MergeAllOperator<T> implements Operator<Observable<T>, T> {
-  constructor(private concurrent: number) {
-  }
-
-  call(observer: Observer<T>, source: any): any {
-    return source.subscribe(new MergeAllSubscriber(observer, this.concurrent));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-export class MergeAllSubscriber<T> extends OuterSubscriber<Observable<T>, T> {
-  private hasCompleted: boolean = false;
-  private buffer: Observable<T>[] = [];
-  private active: number = 0;
-
-  constructor(destination: Observer<T>, private concurrent: number) {
-    super(destination);
-  }
-
-  protected _next(observable: Observable<T>) {
-    if (this.active < this.concurrent) {
-      this.active++;
-      this.add(subscribeToResult<Observable<T>, T>(this, observable));
-    } else {
-      this.buffer.push(observable);
-    }
-  }
-
-  protected _complete() {
-    this.hasCompleted = true;
-    if (this.active === 0 && this.buffer.length === 0) {
-      this.destination.complete();
-    }
-  }
-
-  notifyComplete(innerSub: Subscription) {
-    const buffer = this.buffer;
-    this.remove(innerSub);
-    this.active--;
-    if (buffer.length > 0) {
-      this._next(buffer.shift());
-    } else if (this.active === 0 && this.hasCompleted) {
-      this.destination.complete();
-    }
-  }
+  return <any>higherOrder(concurrent)(this);
 }