1.x: combineLatestDelayError

src/main/java/rx/Observable.java

@@ -906,6 +906,33 @@ public static <T, R> Observable<R> combineLatest(Iterable<? extends Observable<?
         return create(new OnSubscribeCombineLatest<T, R>(sources, combineFunction));
     }
 
+    /**
+     * Combines a collection of source Observables by emitting an item that aggregates the latest values of each of
+     * the source Observables each time an item is received from any of the source Observables, where this
+     * aggregation is defined by a specified function and delays any error from the sources until
+     * all source Observables terminate.
+     * 
+     * <dl>
+     *  <dt><b>Scheduler:</b></dt>
+     *  <dd>{@code combineLatest} does not operate by default on a particular {@link Scheduler}.</dd>
+     * </dl>
+     *
+     * @param <T>
+     *            the common base type of source values
+     * @param <R>
+     *            the result type
+     * @param sources
+     *            the collection of source Observables
+     * @param combineFunction
+     *            the aggregation function used to combine the items emitted by the source Observables
+     * @return an Observable that emits items that are the result of combining the items emitted by the source
+     *         Observables by means of the given aggregation function
+     * @see <a href="http://reactivex.io/documentation/operators/combinelatest.html">ReactiveX operators documentation: CombineLatest</a>
+     */
+    public static <T, R> Observable<R> combineLatestDelayError(Iterable<? extends Observable<? extends T>> sources, FuncN<? extends R> combineFunction) {
+        return create(new OnSubscribeCombineLatest<T, R>(null, sources, combineFunction, RxRingBuffer.SIZE, true));
+    }
+
     /**
      * Returns an Observable that emits the items emitted by each of the Observables emitted by the source
      * Observable, one after the other, without interleaving them.

src/main/java/rx/internal/operators/OnSubscribeCombineLatest.java

@@ -213,7 +213,7 @@ void combine(Object value, int index) {
                     if (value != null && allSourcesFinished) {
                         queue.offer(combinerSubscriber, latest.clone());
                     } else
-                    if (value == null && error.get() != null) {
+                    if (value == null && error.get() != null && (o == MISSING || !delayError)) {
                         done = true; // if this source completed without a value
                     }
                 } else {

src/test/java/rx/internal/operators/OnSubscribeCombineLatestTest.java

@@ -29,6 +29,7 @@
 import rx.*;
 import rx.Observable;
 import rx.Observer;
+import rx.exceptions.*;
 import rx.functions.*;
 import rx.internal.util.RxRingBuffer;
 import rx.observers.TestSubscriber;
@@ -954,5 +955,107 @@ public Integer call(Object... args) {
             throw new RuntimeException();
         }
 
-    }; 
+    };
+
+    @SuppressWarnings("unchecked")
+    @Test
+    public void firstJustError() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+
+        Observable.combineLatestDelayError(
+                Arrays.asList(Observable.just(1), Observable.<Integer>error(new TestException())),
+                new FuncN<Integer>() {
+                    @Override
+                    public Integer call(Object... args) {
+                        return ((Integer)args[0]) + ((Integer)args[1]);
+                    }
+                }
+        ).subscribe(ts);
+
+        ts.assertNoValues();
+        ts.assertError(TestException.class);
+        ts.assertNotCompleted();
+    }
+
+    @SuppressWarnings("unchecked")
+    @Test
+    public void secondJustError() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+
+        Observable.combineLatestDelayError(
+                Arrays.asList(Observable.<Integer>error(new TestException()), Observable.just(1)),
+                new FuncN<Integer>() {
+                    @Override
+                    public Integer call(Object... args) {
+                        return ((Integer)args[0]) + ((Integer)args[1]);
+                    }
+                }
+        ).subscribe(ts);
+
+        ts.assertNoValues();
+        ts.assertError(TestException.class);
+        ts.assertNotCompleted();
+    }
+
+    @SuppressWarnings("unchecked")
+    @Test
+    public void oneErrors() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+
+        Observable.combineLatestDelayError(
+                Arrays.asList(Observable.just(10).concatWith(Observable.<Integer>error(new TestException())), Observable.just(1)),
+                new FuncN<Integer>() {
+                    @Override
+                    public Integer call(Object... args) {
+                        return ((Integer)args[0]) + ((Integer)args[1]);
+                    }
+                }
+        ).subscribe(ts);
+
+        ts.assertValues(11);
+        ts.assertError(TestException.class);
+        ts.assertNotCompleted();
+    }
+
+    @SuppressWarnings("unchecked")
+    @Test
+    public void twoErrors() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+
+        Observable.combineLatestDelayError(
+                Arrays.asList(Observable.just(1), Observable.just(10).concatWith(Observable.<Integer>error(new TestException()))),
+                new FuncN<Integer>() {
+                    @Override
+                    public Integer call(Object... args) {
+                        return ((Integer)args[0]) + ((Integer)args[1]);
+                    }
+                }
+        ).subscribe(ts);
+
+        ts.assertValues(11);
+        ts.assertError(TestException.class);
+        ts.assertNotCompleted();
+    }
+
+    @SuppressWarnings("unchecked")
+    @Test
+    public void bothError() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+
+        Observable.combineLatestDelayError(
+                Arrays.asList(Observable.just(1).concatWith(Observable.<Integer>error(new TestException())), 
+                        Observable.just(10).concatWith(Observable.<Integer>error(new TestException()))),
+                new FuncN<Integer>() {
+                    @Override
+                    public Integer call(Object... args) {
+                        return ((Integer)args[0]) + ((Integer)args[1]);
+                    }
+                }
+        ).subscribe(ts);
+
+        ts.assertValues(11);
+        ts.assertError(CompositeException.class);
+        ts.assertNotCompleted();
+    }
+
 }