feat(operator): Add expand operator.

spec/operators/expand-spec.js

@@ -0,0 +1,29 @@
+var Rx = require('../../dist/cjs/Rx');
+var Observable = Rx.Observable;
+
+describe('Observable.prototype.expand()', function () {
+  it('should map and recursively flatten', function (done) {
+    var expected = [1, 2, 3, 4, 5];
+    Observable.of(0).expand(function (x) {
+      if (x > 4) {
+        return Observable.empty();
+      }
+      return Observable.of(x + 1);
+    })
+    .subscribe(function (x) {
+      expect(x).toBe(expected.shift());
+    }, null, done);
+  });
+  it('should map and recursively flatten with ScalarObservables', function (done) {
+    var expected = [1, 2, 3, 4, 5];
+    Observable.return(0).expand(function (x) {
+      if (x > 4) {
+        return Observable.empty();
+      }
+      return Observable.return(x + 1);
+    })
+    .subscribe(function (x) {
+      expect(x).toBe(expected.shift());
+    }, null, done);
+  });
+});

src/Observable.ts

@@ -107,6 +107,8 @@ export default class Observable<T> {
                  projectResult?: (x: T, y: any, ix: number, iy: number) => R,
                  concurrent?: number) => Observable<R>;
 
+  expand: (project: (x: T, ix: number) => Observable<any>) => Observable<any>;
+
   switchAll: <R>() => Observable<R>;
   switchLatest: <R>(project: ((x: T, ix: number) => Observable<any>),
                     projectResult?: (x: T, y: any, ix: number, iy: number) => R) => Observable<R>;

src/Rx.ts

@@ -63,6 +63,7 @@ import flatMapTo from './operators/flatMapTo';
 import switchAll from './operators/switchAll';
 import switchLatest from './operators/switchLatest';
 import switchLatestTo from './operators/switchLatestTo';
+import expand from './operators/expand';
 
 Observable.merge = merge;
 observableProto.merge = merge;
@@ -72,6 +73,7 @@ observableProto.flatMapTo = flatMapTo;
 observableProto.switchAll = switchAll;
 observableProto.switchLatest = switchLatest;
 observableProto.switchLatestTo = switchLatestTo;
+observableProto.expand = expand;
 
 import map from './operators/map';
 import mapTo from './operators/mapTo';

src/operators/expand.ts

@@ -0,0 +1,71 @@
+import Operator from '../Operator';
+import Observer from '../Observer';
+import Observable from '../Observable';
+import Subscriber from '../Subscriber';
+
+import {MergeSubscriber, MergeInnerSubscriber} from './merge';
+import EmptyObservable from '../observables/EmptyObservable';
+import ScalarObservable from '../observables/ScalarObservable';
+
+import tryCatch from '../util/tryCatch';
+import {errorObject} from '../util/errorObject';
+
+export default function expand<T>(project: (x: T, ix: number) => Observable<any>): Observable<any> {
+  return this.lift(new ExpandOperator(project));
+}
+
+export class ExpandOperator<T, R> extends Operator<T, R> {
+
+  project: (x: T, ix: number) => Observable<any>;
+
+  constructor(project: (x: T, ix: number) => Observable<any>) {
+    super();
+    this.project = project;
+  }
+
+  call(observer: Observer<R>): Observer<T> {
+    return new ExpandSubscriber(observer, this.project);
+  }
+}
+
+export class ExpandSubscriber<T, R> extends MergeSubscriber<T, R> {
+
+  project: (x: T, ix: number) => Observable<any>;
+
+  constructor(destination: Observer<R>,
+              project: (x: T, ix: number) => Observable<any>) {
+    super(destination, Number.POSITIVE_INFINITY);
+    this.project = project;
+  }
+
+  _project(value, index) {
+    const observable = tryCatch(this.project).call(this, value, index);
+    if (observable === errorObject) {
+      this.error(errorObject.e);
+      return null;
+    }
+    return observable;
+  }
+
+  _subscribeInner(observable, value, index) {
+    if(observable instanceof ScalarObservable) {
+      this.destination.next((<ScalarObservable<T>> observable).value);
+      this._innerComplete();
+      this._next((<ScalarObservable<T>> observable).value);
+    } else if(observable instanceof EmptyObservable) {
+      this._innerComplete();
+    } else {
+      return observable.subscribe(new ExpandInnerSubscriber(this));
+    }
+  }
+}
+
+export class ExpandInnerSubscriber<T, R> extends MergeInnerSubscriber<T, R> {
+  constructor(parent: ExpandSubscriber<T, R>) {
+    super(parent);
+  }
+  _next(value) {
+    this.destination.next(value);
+    this.parent.next(value);
+  }
+}