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

src/operator/share.ts

@@ -1,10 +1,5 @@
 import { Observable } from '../Observable';
-import { multicast } from './multicast';
-import { Subject } from '../Subject';
-
-function shareSubjectFactory() {
-  return new Subject();
-}
+import { share as higherOrder } from '../operators/share';
 
 /**
  * Returns a new Observable that multicasts (shares) the original Observable. As long as there is at least one
@@ -19,5 +14,5 @@ function shareSubjectFactory() {
  * @owner Observable
  */
 export function share<T>(this: Observable<T>): Observable<T> {
-  return multicast.call(this, shareSubjectFactory).refCount();
+  return higherOrder()(this);
 };

src/operators/index.ts

@@ -62,6 +62,7 @@ export { sample } from './sample';
 export { sampleTime } from './sampleTime';
 export { scan } from './scan';
 export { sequenceEqual } from './sequenceEqual';
+export { share } from './share';
 export { subscribeOn } from './subscribeOn';
 export { switchAll } from './switchAll';
 export { switchMap } from './switchMap';

src/operators/share.ts

@@ -0,0 +1,26 @@
+import { Observable } from '../Observable';
+import { multicast } from './multicast';
+import { refCount } from './refCount';
+import { Subject } from '../Subject';
+
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+function shareSubjectFactory() {
+  return new Subject();
+}
+
+/**
+ * Returns a new Observable that multicasts (shares) the original Observable. As long as there is at least one
+ * Subscriber this Observable will be subscribed and emitting data. When all subscribers have unsubscribed it will
+ * unsubscribe from the source Observable. Because the Observable is multicasting it makes the stream `hot`.
+ * This is an alias for .publish().refCount().
+ *
+ * <img src="./img/share.png" width="100%">
+ *
+ * @return {Observable<T>} An Observable that upon connection causes the source Observable to emit items to its Observers.
+ * @method share
+ * @owner Observable
+ */
+export function share<T>(): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => refCount()(multicast(shareSubjectFactory)(source));
+};