refactor: Improve memory pressure

this is the duplicate of ReactiveX#5610, it is refactoring to ensure outer values are not retained when they do not have to be. It needs to be done in a separate PR because the branches diverge just enough to require it. This PR also has some mild, internal type fixes.

src/internal/innerSubscribe.ts

@@ -0,0 +1,114 @@
+/** @prettier */
+import { Subscription } from './Subscription';
+import { Subscriber } from './Subscriber';
+import { Observable } from './Observable';
+import { subscribeTo } from './util/subscribeTo';
+
+interface SimpleOuterSubscriberLike<T> {
+  /**
+   * A handler for inner next notifications from the inner subscription
+   * @param innerValue the value nexted by the inner producer
+   */
+  notifyNext(innerValue: T): void;
+  /**
+   * A handler for inner error notifications from the inner subscription
+   * @param err the error from the inner producer
+   */
+  notifyError(err: any): void;
+  /**
+   * A handler for inner complete notifications from the inner subscription.
+   */
+  notifyComplete(): void;
+}
+
+export class SimpleInnerSubscriber<T> extends Subscriber<T> {
+  constructor(private parent: SimpleOuterSubscriberLike<any>) {
+    super();
+  }
+
+  protected _next(value: T): void {
+    this.parent.notifyNext(value);
+  }
+
+  protected _error(error: any): void {
+    this.parent.notifyError(error);
+    this.unsubscribe();
+  }
+
+  protected _complete(): void {
+    this.parent.notifyComplete();
+    this.unsubscribe();
+  }
+}
+
+export class ComplexInnerSubscriber<T, R> extends Subscriber<R> {
+  constructor(private parent: ComplexOuterSubscriber<T, R>, public outerValue: T, public outerIndex: number) {
+    super();
+  }
+
+  protected _next(value: R): void {
+    this.parent.notifyNext(this.outerValue, value, this.outerIndex, this);
+  }
+
+  protected _error(error: any): void {
+    this.parent.notifyError(error);
+    this.unsubscribe();
+  }
+
+  protected _complete(): void {
+    this.parent.notifyComplete(this);
+    this.unsubscribe();
+  }
+}
+
+export class SimpleOuterSubscriber<T, R> extends Subscriber<T> implements SimpleOuterSubscriberLike<R> {
+  notifyNext(innerValue: R): void {
+    this.destination.next(innerValue);
+  }
+
+  notifyError(err: any): void {
+    this.destination.error(err);
+  }
+
+  notifyComplete(): void {
+    this.destination.complete();
+  }
+}
+
+/**
+ * DO NOT USE (formerly "OuterSubscriber")
+ * TODO: We want to refactor this and remove it. It is retaining values it shouldn't for long
+ * periods of time.
+ */
+export class ComplexOuterSubscriber<T, R> extends Subscriber<T> {
+  /**
+   * @param _outerValue Used by: bufferToggle, delayWhen, windowToggle
+   * @param innerValue Used by: subclass default, combineLatest, race, bufferToggle, windowToggle, withLatestFrom
+   * @param _outerIndex Used by: combineLatest, race, withLatestFrom
+   * @param _innerSub Used by: delayWhen
+   */
+  notifyNext(_outerValue: T, innerValue: R, _outerIndex: number, _innerSub: ComplexInnerSubscriber<T, R>): void {
+    this.destination.next(innerValue);
+  }
+
+  notifyError(error: any): void {
+    this.destination.error(error);
+  }
+
+  /**
+   * @param _innerSub Used by: race, bufferToggle, delayWhen, windowToggle, windowWhen
+   */
+  notifyComplete(_innerSub: ComplexInnerSubscriber<T, R>): void {
+    this.destination.complete();
+  }
+}
+
+export function innerSubscribe(result: any, innerSubscriber: Subscriber<any>): Subscription | undefined {
+  if (innerSubscriber.closed) {
+    return undefined;
+  }
+  if (result instanceof Observable) {
+    return result.subscribe(innerSubscriber);
+  }
+  return subscribeTo(result)(innerSubscriber) as Subscription;
+}

src/internal/observable/combineLatest.ts

@@ -226,8 +226,8 @@ export function combineLatest<R>(...observables: Array<ObservableInput<any> | ((
 export function combineLatest<O extends ObservableInput<any>, R>(
   ...observables: (O | ((...values: ObservedValueOf<O>[]) => R) | SchedulerLike)[]
 ): Observable<R> {
-  let resultSelector: (...values: Array<any>) => R =  null;
-  let scheduler: SchedulerLike = null;
+  let resultSelector: ((...values: Array<any>) => R) | undefined =  undefined;
+  let scheduler: SchedulerLike|undefined = undefined;
 
   if (isScheduler(observables[observables.length - 1])) {
     scheduler = observables.pop() as SchedulerLike;
@@ -243,7 +243,7 @@ export function combineLatest<O extends ObservableInput<any>, R>(
     observables = observables[0] as any;
   }
 
-  return fromArray(observables, scheduler).lift(new CombineLatestOperator<ObservedValueOf<O>, R>(resultSelector));
+  return fromArray(observables, scheduler).lift(new CombineLatestOperator(resultSelector));
 }
 
 export class CombineLatestOperator<T, R> implements Operator<T, R> {
@@ -264,7 +264,7 @@ export class CombineLatestSubscriber<T, R> extends OuterSubscriber<T, R> {
   private active: number = 0;
   private values: any[] = [];
   private observables: any[] = [];
-  private toRespond: number;
+  private toRespond?: number;
 
   constructor(destination: Subscriber<R>, private resultSelector?: (...values: Array<any>) => R) {
     super(destination);
@@ -279,26 +279,25 @@ export class CombineLatestSubscriber<T, R> extends OuterSubscriber<T, R> {
     const observables = this.observables;
     const len = observables.length;
     if (len === 0) {
-      this.destination.complete();
+      this.destination.complete!();
     } else {
       this.active = len;
       this.toRespond = len;
       for (let i = 0; i < len; i++) {
         const observable = observables[i];
-        this.add(subscribeToResult(this, observable, observable, i));
+        this.add(subscribeToResult(this, observable, undefined, i));
       }
     }
   }
 
   notifyComplete(unused: Subscriber<R>): void {
     if ((this.active -= 1) === 0) {
-      this.destination.complete();
+      this.destination.complete!();
     }
   }
 
-  notifyNext(outerValue: T, innerValue: R,
-             outerIndex: number, innerIndex: number,
-             innerSub: InnerSubscriber<T, R>): void {
+  notifyNext(_outerValue: T, innerValue: R,
+             outerIndex: number): void {
     const values = this.values;
     const oldVal = values[outerIndex];
     const toRespond = !this.toRespond
@@ -310,19 +309,19 @@ export class CombineLatestSubscriber<T, R> extends OuterSubscriber<T, R> {
       if (this.resultSelector) {
         this._tryResultSelector(values);
       } else {
-        this.destination.next(values.slice());
+        this.destination.next!(values.slice());
       }
     }
   }
 
   private _tryResultSelector(values: any[]) {
     let result: any;
     try {
-      result = this.resultSelector.apply(this, values);
+      result = this.resultSelector!.apply(this, values);
     } catch (err) {
-      this.destination.error(err);
+      this.destination.error!(err);
       return;
     }
-    this.destination.next(result);
+    this.destination.next!(result);
   }
 }

src/internal/observable/race.ts

@@ -102,24 +102,23 @@ export class RaceSubscriber<T> extends OuterSubscriber<T, T> {
     const len = observables.length;
 
     if (len === 0) {
-      this.destination.complete();
+      this.destination.complete!();
     } else {
       for (let i = 0; i < len && !this.hasFirst; i++) {
-        let observable = observables[i];
-        let subscription = subscribeToResult(this, observable, observable as any, i);
+        const observable = observables[i];
+        const subscription = subscribeToResult(this, observable, undefined, i)!;
 
         if (this.subscriptions) {
           this.subscriptions.push(subscription);
         }
         this.add(subscription);
       }
-      this.observables = null;
+      this.observables = null!;
     }
   }
 
-  notifyNext(outerValue: T, innerValue: T,
-             outerIndex: number, innerIndex: number,
-             innerSub: InnerSubscriber<T, T>): void {
+  notifyNext(_outerValue: T, innerValue: T,
+             outerIndex: number): void {
     if (!this.hasFirst) {
       this.hasFirst = true;
 
@@ -132,9 +131,9 @@ export class RaceSubscriber<T> extends OuterSubscriber<T, T> {
         }
       }
 
-      this.subscriptions = null;
+      this.subscriptions = null!;
     }
 
-    this.destination.next(innerValue);
+    this.destination.next!(innerValue);
   }
 }