Merge pull request ReactiveX#1577 from zsxwing/compose-covariance

Fix the compose covariance

Author: benjchristensen

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

@@ -204,7 +204,7 @@ public void call(Subscriber<? super R> o) {
      * @see <a href="https://github.com/Netflix/RxJava/wiki/Implementing-Your-Own-Operators">RxJava wiki: Implementing Your Own Operators</a>
      * @since 0.20
      */
-    public <R> Observable<? extends R> compose(Transformer<? super T, ? extends R> transformer) {
+    public <R> Observable<R> compose(Transformer<? super T, R> transformer) {
         return transformer.call(this);
     }
 
@@ -213,7 +213,7 @@ public <R> Observable<? extends R> compose(Transformer<? super T, ? extends R> t
      * @warn more complete description needed
      * @since 0.20
      */
-    public static interface Transformer<T, R> extends Func1<Observable<? extends T>, Observable<? extends R>> {
+    public static interface Transformer<T, R> extends Func1<Observable<? extends T>, Observable<R>> {
         // cover for generics insanity
     }
 

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

@@ -62,10 +62,10 @@ public Integer call(Media t1, Media t2) {
     @Test
     public void testCovarianceOfCompose() {
         Observable<HorrorMovie> movie = Observable.<HorrorMovie> from(new HorrorMovie());
-        movie.compose(new Transformer<Movie, Movie>() {
+        Observable<Movie> movie2 = movie.compose(new Transformer<Movie, Movie>() {
 
             @Override
-            public Observable<? extends Movie> call(Observable<? extends Movie> t1) {
+            public Observable<Movie> call(Observable<? extends Movie> t1) {
                 return Observable.from(new Movie());
             }
 
@@ -75,9 +75,9 @@ public Observable<? extends Movie> call(Observable<? extends Movie> t1) {
     @Test
     public void testCovarianceOfCompose2() {
         Observable<Movie> movie = Observable.<Movie> from(new HorrorMovie());
-        movie.compose(new Transformer<Movie, Movie>() {
+        Observable<HorrorMovie> movie2 = movie.compose(new Transformer<Movie, HorrorMovie>() {
             @Override
-            public Observable<? extends Movie> call(Observable<? extends Movie> t1) {
+            public Observable<HorrorMovie> call(Observable<? extends Movie> t1) {
                 return Observable.from(new HorrorMovie());
             }
         });

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

@@ -1108,7 +1108,7 @@ public void testCompose() {
         Observable.from(1, 2, 3).compose(new Transformer<Integer, String>() {
 
             @Override
-            public Observable<? extends String> call(Observable<? extends Integer> t1) {
+            public Observable<String> call(Observable<? extends Integer> t1) {
                 return t1.map(new Func1<Integer, String>() {
 
                     @Override