Merge pull request #3365 from benlesh/refactor-using

refactor(using): using is now just a function

spec/observables/using-spec.ts

@@ -1,15 +1,12 @@
 import { expect } from 'chai';
-import * as Rx from '../../src/internal/Rx';
+import { using, range, Subscription } from '../../src';
 
-const Observable = Rx.Observable;
-const Subscription = Rx.Subscription;
-
-describe('Observable.using', () => {
+describe('using', () => {
   it('should dispose of the resource when the subscription is disposed', (done) => {
     let disposed = false;
-    const source = Observable.using(
+    const source = using(
       () => new Subscription(() => disposed = true),
-      (resource) => Observable.range(0, 3)
+      (resource) => range(0, 3)
     )
     .take(2);
 
@@ -26,7 +23,7 @@ describe('Observable.using', () => {
     const expected = 42;
 
     let disposed = false;
-    const e1 = Observable.using(
+    const e1 = using(
       () => new Subscription(() => disposed = true),
       (resource) => new Promise((resolve: any) => { resolve(expected); }));
 
@@ -43,7 +40,7 @@ describe('Observable.using', () => {
     const expected = 42;
 
     let disposed = false;
-    const e1 = Observable.using(
+    const e1 = using(
       () => new Subscription(() => disposed = true),
       (resource) => new Promise((resolve: any, reject: any) => { reject(expected); }));
 
@@ -61,7 +58,7 @@ describe('Observable.using', () => {
     const expectedError = 'expected';
     const error = 'error';
 
-    const source = Observable.using(
+    const source = using(
       () => {
         throw expectedError;
       },
@@ -84,7 +81,7 @@ describe('Observable.using', () => {
     const error = 'error';
     let disposed = false;
 
-    const source = Observable.using(
+    const source = using(
       () => new Subscription(() => disposed = true),
       (resource) => {
         throw error;

src/internal/observable/using.ts

@@ -1,3 +1,63 @@
-import {  UsingObservable  } from './UsingObservable';
+import { Observable } from '../Observable';
+import { Unsubscribable, ObservableInput } from '../types';
+import { from } from './from'; // from from from! LAWL
+import { EMPTY } from './empty';
 
-export const using = UsingObservable.create;
+/**
+ * Creates an Observable that uses a resource which will be disposed at the same time as the Observable.
+ *
+ * <span class="informal">Use it when you catch yourself cleaning up after an Observable.</span>
+ *
+ * `using` is a factory operator, which accepts two functions. First function returns a disposable resource.
+ * It can be an arbitrary object that implements `unsubscribe` method. Second function will be injected with
+ * that object and should return an Observable. That Observable can use resource object during its execution.
+ * Both functions passed to `using` will be called every time someone subscribes - neither an Observable nor
+ * resource object will be shared in any way between subscriptions.
+ *
+ * When Observable returned by `using` is subscribed, Observable returned from the second function will be subscribed
+ * as well. All its notifications (nexted values, completion and error events) will be emitted unchanged by the output
+ * Observable. If however someone unsubscribes from the Observable or source Observable completes or errors by itself,
+ * the `unsubscribe` method on resource object will be called. This can be used to do any necessary clean up, which
+ * otherwise would have to be handled by hand. Note that complete or error notifications are not emitted when someone
+ * cancels subscription to an Observable via `unsubscribe`, so `using` can be used as a hook, allowing you to make
+ * sure that all resources which need to exist during an Observable execution will be disposed at appropriate time.
+ *
+ * @see {@link defer}
+ *
+ * @param {function(): ISubscription} resourceFactory A function which creates any resource object
+ * that implements `unsubscribe` method.
+ * @param {function(resource: ISubscription): Observable<T>} observableFactory A function which
+ * creates an Observable, that can use injected resource object.
+ * @return {Observable<T>} An Observable that behaves the same as Observable returned by `observableFactory`, but
+ * which - when completed, errored or unsubscribed - will also call `unsubscribe` on created resource object.
+ */
+export function using<T>(resourceFactory: () => Unsubscribable | void,
+                         observableFactory: (resource: Unsubscribable | void) => ObservableInput<T> | void): Observable<T> {
+  return new Observable<T>(subscriber => {
+    let resource: Unsubscribable | void;
+
+    try {
+      resource = resourceFactory();
+    } catch (err) {
+      subscriber.error(err);
+      return undefined;
+    }
+
+    let result: ObservableInput<T> | void;
+    try {
+      result = observableFactory(resource);
+    } catch (err) {
+      subscriber.error(err);
+      return undefined;
+    }
+
+    const source = result ? from(result) : EMPTY;
+    const subscription = source.subscribe(subscriber);
+    return () => {
+      subscription.unsubscribe();
+      if (resource) {
+        resource.unsubscribe();
+      }
+    };
+  });
+}