initial commit: scaffolding

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diff --git a/node_modules/rxjs/src/internal/observable/using.ts b/node_modules/rxjs/src/internal/observable/using.ts
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+import { Observable } from '../Observable';
+import { Unsubscribable, ObservableInput, ObservedValueOf } from '../types';
+import { innerFrom } from './innerFrom';
+import { EMPTY } from './empty';
+
+/**
+ * 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 resourceFactory A function which creates any resource object that implements `unsubscribe` method.
+ * @param observableFactory A function which creates an Observable, that can use injected resource object.
+ * @return 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 extends ObservableInput<any>>(
+  resourceFactory: () => Unsubscribable | void,
+  observableFactory: (resource: Unsubscribable | void) => T | void
+): Observable<ObservedValueOf<T>> {
+  return new Observable<ObservedValueOf<T>>((subscriber) => {
+    const resource = resourceFactory();
+    const result = observableFactory(resource);
+    const source = result ? innerFrom(result) : EMPTY;
+    source.subscribe(subscriber);
+    return () => {
+      // NOTE: Optional chaining did not work here.
+      // Related TS Issue: https://github.com/microsoft/TypeScript/issues/40818
+      if (resource) {
+        resource.unsubscribe();
+      }
+    };
+  });
+}