feat(combineAll): add higher-order lettable version of combineAll

src/operator/combineAll.ts

@@ -1,5 +1,6 @@
-import { CombineLatestOperator } from '../operators/combineLatest';
+
 import { Observable } from '../Observable';
+import { combineAll as higherOrder } from '../operators';
 
 /**
  * Converts a higher-order Observable into a first-order Observable by waiting
@@ -42,5 +43,5 @@ import { Observable } from '../Observable';
  * @owner Observable
  */
 export function combineAll<T, R>(this: Observable<T>, project?: (...values: Array<any>) => R): Observable<R> {
-  return this.lift(new CombineLatestOperator(project));
+  return higherOrder(project)(this);
 }

src/operators/combineAll.ts

@@ -0,0 +1,7 @@
+import { CombineLatestOperator } from '../operators/combineLatest';
+import { Observable } from '../Observable';
+import { OperatorFunction } from '../interfaces';
+
+export function combineAll<T, R>(project?: (...values: Array<any>) => R): OperatorFunction<T, R> {
+  return (source: Observable<T>) => source.lift(new CombineLatestOperator(project));
+}

src/operators/index.ts

@@ -6,6 +6,7 @@ export { bufferTime } from './bufferTime';
 export { bufferToggle } from './bufferToggle';
 export { bufferWhen } from './bufferWhen';
 export { catchError } from './catchError';
+export { combineAll } from './combineAll';
 export { combineLatest } from './combineLatest';
 export { concat } from './concat';
 export { concatAll } from './concatAll';