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

src/operator/retry.ts

@@ -1,7 +1,5 @@
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
 import { Observable } from '../Observable';
-import { TeardownLogic } from '../Subscription';
+import { retry as higherOrder } from '../operators/retry';
 
 /**
  * Returns an Observable that mirrors the source Observable with the exception of an `error`. If the source Observable
@@ -20,39 +18,5 @@ import { TeardownLogic } from '../Subscription';
  * @owner Observable
  */
 export function retry<T>(this: Observable<T>, count: number = -1): Observable<T> {
-  return this.lift(new RetryOperator(count, this));
-}
-
-class RetryOperator<T> implements Operator<T, T> {
-  constructor(private count: number,
-              private source: Observable<T>) {
-  }
-
-  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
-    return source.subscribe(new RetrySubscriber(subscriber, this.count, this.source));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class RetrySubscriber<T> extends Subscriber<T> {
-  constructor(destination: Subscriber<any>,
-              private count: number,
-              private source: Observable<T>) {
-    super(destination);
-  }
-  error(err: any) {
-    if (!this.isStopped) {
-      const { source, count } = this;
-      if (count === 0) {
-        return super.error(err);
-      } else if (count > -1) {
-        this.count = count - 1;
-      }
-      source.subscribe(this._unsubscribeAndRecycle());
-    }
-  }
+  return higherOrder(count)(this);
 }

src/operators/index.ts

@@ -55,6 +55,7 @@ export { race } from './race';
 export { reduce } from './reduce';
 export { repeat } from './repeat';
 export { repeatWhen } from './repeatWhen';
+export { retry } from './retry';
 export { refCount } from './refCount';
 export { scan } from './scan';
 export { subscribeOn } from './subscribeOn';

src/operators/retry.ts

@@ -0,0 +1,60 @@
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { Observable } from '../Observable';
+import { TeardownLogic } from '../Subscription';
+
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * Returns an Observable that mirrors the source Observable with the exception of an `error`. If the source Observable
+ * calls `error`, this method will resubscribe to the source Observable for a maximum of `count` resubscriptions (given
+ * as a number parameter) rather than propagating the `error` call.
+ *
+ * <img src="./img/retry.png" width="100%">
+ *
+ * Any and all items emitted by the source Observable will be emitted by the resulting Observable, even those emitted
+ * during failed subscriptions. For example, if an Observable fails at first but emits [1, 2] then succeeds the second
+ * time and emits: [1, 2, 3, 4, 5] then the complete stream of emissions and notifications
+ * would be: [1, 2, 1, 2, 3, 4, 5, `complete`].
+ * @param {number} count - Number of retry attempts before failing.
+ * @return {Observable} The source Observable modified with the retry logic.
+ * @method retry
+ * @owner Observable
+ */
+export function retry<T>(count: number = -1): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => source.lift(new RetryOperator(count, source));
+}
+
+class RetryOperator<T> implements Operator<T, T> {
+  constructor(private count: number,
+              private source: Observable<T>) {
+  }
+
+  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+    return source.subscribe(new RetrySubscriber(subscriber, this.count, this.source));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class RetrySubscriber<T> extends Subscriber<T> {
+  constructor(destination: Subscriber<any>,
+              private count: number,
+              private source: Observable<T>) {
+    super(destination);
+  }
+  error(err: any) {
+    if (!this.isStopped) {
+      const { source, count } = this;
+      if (count === 0) {
+        return super.error(err);
+      } else if (count > -1) {
+        this.count = count - 1;
+      }
+      source.subscribe(this._unsubscribeAndRecycle());
+    }
+  }
+}