feat(publishBehavior): add higher-order lettable version of publishBe…

…havior

src/operator/publishBehavior.ts

@@ -1,7 +1,6 @@
 import { Observable } from '../Observable';
-import { BehaviorSubject } from '../BehaviorSubject';
-import { multicast } from './multicast';
 import { ConnectableObservable } from '../observable/ConnectableObservable';
+import {publishBehavior as higherOrder } from '../operators/publishBehavior';
 
 /**
  * @param value
@@ -10,5 +9,5 @@ import { ConnectableObservable } from '../observable/ConnectableObservable';
  * @owner Observable
  */
 export function publishBehavior<T>(this: Observable<T>, value: T): ConnectableObservable<T> {
-  return multicast.call(this, new BehaviorSubject<T>(value));
+  return higherOrder(value)(this);
 }

src/operators/index.ts

@@ -50,6 +50,7 @@ export { pairwise } from './pairwise';
 export { partition } from './partition';
 export { pluck } from './pluck';
 export { publish } from './publish';
+export { publishBehavior } from './publishBehavior';
 export { race } from './race';
 export { reduce } from './reduce';
 export { refCount } from './refCount';

src/operators/publishBehavior.ts

@@ -0,0 +1,15 @@
+import { Observable } from '../Observable';
+import { BehaviorSubject } from '../BehaviorSubject';
+import { multicast } from './multicast';
+import { ConnectableObservable } from '../observable/ConnectableObservable';
+import { UnaryFunction } from '../interfaces';
+
+/**
+ * @param value
+ * @return {ConnectableObservable<T>}
+ * @method publishBehavior
+ * @owner Observable
+ */
+export function publishBehavior<T>(value: T):  UnaryFunction<Observable<T>, ConnectableObservable<T>> {
+  return (source: Observable<T>) => multicast(new BehaviorSubject<T>(value))(source) as ConnectableObservable<T>;
+}