Implemented Observable#toCompletable

src/main/java/rx/Completable.java

@@ -568,7 +568,7 @@ public void onNext(Object t) {
                     }
                 };
                 cs.onSubscribe(subscriber);
-                flowable.subscribe(subscriber);
+                flowable.unsafeSubscribe(subscriber);
             }
         });
     }

src/main/java/rx/Observable.java

@@ -232,6 +232,31 @@ public Single<T> toSingle() {
         return new Single<T>(OnSubscribeSingle.create(this));
     }
 
+    /**
+     * Returns a Completable that discards all onNext emissions (similar to
+     * {@code ignoreAllElements()}) and calls onCompleted when this source observable calls
+     * onCompleted. Error terminal events are propagated.
+     * <p>
+     * <img width="640" height="295" src=
+     * "https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Completable.toCompletable.png"
+     * alt="">
+     * <dl>
+     * <dt><b>Scheduler:</b></dt>
+     * <dd>{@code toCompletable} does not operate by default on a particular {@link Scheduler}.</dd>
+     * </dl>
+     *
+     * @return a Completable that calls onCompleted on it's subscriber when the source Observable
+     *         calls onCompleted
+     * @see <a href="http://reactivex.io/documentation/completable.html">ReactiveX documentation:
+     *      Completable</a>
+     * @since (if this graduates from Experimental/Beta to supported, replace this parenthetical
+     *        with the release number)
+     */
+    @Experimental
+    public Completable toCompletable() {
+        return Completable.fromObservable(this);
+    }
+
 
     /* *********************************************************************************************************
      * Operators Below Here

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

@@ -0,0 +1,98 @@
+/**
+ * Copyright 2014 Netflix, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package rx.internal.operators;
+
+import static org.junit.Assert.assertFalse;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.junit.Test;
+
+import rx.Completable;
+import rx.Observable;
+import rx.functions.Action0;
+import rx.observers.TestSubscriber;
+
+public class OnSubscribeCompletableTest {
+
+    @Test
+    public void testJustSingleItemObservable() {
+        TestSubscriber<String> subscriber = TestSubscriber.create();
+        Completable cmp = Observable.just("Hello World!").toCompletable();
+        cmp.subscribe(subscriber);
+
+        subscriber.assertNoValues();
+        subscriber.assertCompleted();
+        subscriber.assertNoErrors();
+    }
+
+    @Test
+    public void testErrorObservable() {
+        TestSubscriber<String> subscriber = TestSubscriber.create();
+        IllegalArgumentException error = new IllegalArgumentException("Error");
+        Completable cmp = Observable.<String>error(error).toCompletable();
+        cmp.subscribe(subscriber);
+
+        subscriber.assertError(error);
+        subscriber.assertNoValues();
+    }
+
+    @Test
+    public void testJustTwoEmissionsObservableThrowsError() {
+        TestSubscriber<String> subscriber = TestSubscriber.create();
+        Completable cmp = Observable.just("First", "Second").toCompletable();
+        cmp.subscribe(subscriber);
+
+        subscriber.assertNoErrors();
+        subscriber.assertNoValues();
+    }
+
+    @Test
+    public void testEmptyObservable() {
+        TestSubscriber<String> subscriber = TestSubscriber.create();
+        Completable cmp = Observable.<String>empty().toCompletable();
+        cmp.subscribe(subscriber);
+
+        subscriber.assertNoErrors();
+        subscriber.assertNoValues();
+        subscriber.assertCompleted();
+    }
+
+    @Test
+    public void testNeverObservable() {
+        TestSubscriber<String> subscriber = TestSubscriber.create();
+        Completable cmp = Observable.<String>never().toCompletable();
+        cmp.subscribe(subscriber);
+
+        subscriber.assertNoTerminalEvent();
+        subscriber.assertNoValues();
+    }
+
+    @Test
+    public void testShouldUseUnsafeSubscribeInternallyNotSubscribe() {
+        TestSubscriber<String> subscriber = TestSubscriber.create();
+        final AtomicBoolean unsubscribed = new AtomicBoolean(false);
+        Completable cmp = Observable.just("Hello World!").doOnUnsubscribe(new Action0() {
+
+            @Override
+            public void call() {
+                unsubscribed.set(true);
+            }}).toCompletable();
+        cmp.subscribe(subscriber);
+        subscriber.assertCompleted();
+        assertFalse(unsubscribed.get());
+    }
+}