Merge pull request #424 from zsxwing/ignore-elements

Implemented the 'IgnoreElements' operator

Author: benjchristensen

rxjava-core/src/main/java/rx/Observable.java

@@ -4477,6 +4477,17 @@ public Boolean call(T t) {
         }).cast(klass);
     }
 
+    /**
+     * Ignores all values in an observable sequence and only calls onCompleted or onError method.
+     *
+     * @return An empty observable sequence that only call onCompleted, or onError method.
+     *
+     * @see <a href="http://msdn.microsoft.com/en-us/library/hh229242(v=vs.103).aspx">MSDN: Observable.IgnoreElements</a>
+     */
+    public Observable<T> ignoreElements() {
+        return filter(alwaysFalse());
+    }
+
     /**
      * Whether a given {@link Function} is an internal implementation inside rx.* packages or not.
      * <p>

rxjava-core/src/main/java/rx/util/functions/Functions.java

@@ -327,6 +327,10 @@ public static <T> Func1<? super T, Boolean> alwaysTrue() {
         return AlwaysTrue.INSTANCE;
     }
 
+    public static <T> Func1<? super T, Boolean> alwaysFalse() {
+        return AlwaysFalse.INSTANCE;
+    }
+
     public static <T> Func1<T, T> identity() {
         return new Func1<T, T>() {
             @Override
@@ -345,4 +349,12 @@ public Boolean call(Object o) {
         }
     }
 
+    private enum AlwaysFalse implements Func1<Object, Boolean> {
+        INSTANCE;
+
+        @Override
+        public Boolean call(Object o) {
+            return false;
+        }
+    }
 }

rxjava-core/src/test/java/rx/ObservableTests.java

@@ -838,4 +838,15 @@ public void testContainsWithEmptyObservable() {
                 org.mockito.Matchers.any(Throwable.class));
         verify(aObserver, times(1)).onCompleted();
     }
+
+    public void testIgnoreElements() {
+        Observable<Integer> observable = Observable.from(1, 2, 3).ignoreElements();
+
+        @SuppressWarnings("unchecked")
+        Observer<Integer> aObserver = mock(Observer.class);
+        observable.subscribe(aObserver);
+        verify(aObserver, never()).onNext(any(Integer.class));
+        verify(aObserver, never()).onError(any(Throwable.class));
+        verify(aObserver, times(1)).onCompleted();
+    }
 }