Merge pull request #1778 from zsxwing/compose

Change Transformer to Func1<Observable<T>, Observable<R>>

Author: benjchristensen

src/main/java/rx/Observable.java

@@ -174,17 +174,15 @@ public void call(Subscriber<? super R> o) {
      * @return the source Observable, transformed by the transformer function
      * @see <a href="https://github.com/ReactiveX/RxJava/wiki/Implementing-Your-Own-Operators">RxJava wiki: Implementing Your Own Operators</a>
      */
-    @SuppressWarnings("unchecked")
     public <R> Observable<R> compose(Transformer<? super T, ? extends R> transformer) {
-        // Casting to Observable<R> is type-safe because we know Observable is covariant.
-        return (Observable<R>) ((Transformer<T, ? extends R>) transformer).call(this);
+        return ((Transformer<T, R>) transformer).call(this);
     }
 
     /**
      * Transformer function used by {@link #compose}.
      * @warn more complete description needed
      */
-    public static interface Transformer<T, R> extends Func1<Observable<T>, Observable<? extends R>> {
+    public static interface Transformer<T, R> extends Func1<Observable<T>, Observable<R>> {
         // cover for generics insanity
     }
 

src/test/java/rx/CovarianceTest.java

@@ -85,7 +85,7 @@ public Observable<String> call(GroupedObservable<Class<? extends Movie>, Movie>
                 return g.compose(new Transformer<Movie, Movie>() {
 
                     @Override
-                    public Observable<? extends Movie> call(Observable<Movie> m) {
+                    public Observable<Movie> call(Observable<Movie> m) {
                         return m.concatWith(Observable.just(new ActionMovie()));
                     }
 
@@ -112,7 +112,7 @@ public void testCovarianceOfCompose() {
         Observable<Movie> movie2 = movie.compose(new Transformer<Movie, Movie>() {
 
             @Override
-            public Observable<? extends Movie> call(Observable<Movie> t1) {
+            public Observable<Movie> call(Observable<Movie> t1) {
                 return Observable.just(new Movie());
             }
 
@@ -124,7 +124,7 @@ public void testCovarianceOfCompose2() {
         Observable<Movie> movie = Observable.<Movie> just(new HorrorMovie());
         Observable<HorrorMovie> movie2 = movie.compose(new Transformer<Movie, HorrorMovie>() {
             @Override
-            public Observable<? extends HorrorMovie> call(Observable<Movie> t1) {
+            public Observable<HorrorMovie> call(Observable<Movie> t1) {
                 return Observable.just(new HorrorMovie());
             }
         });
@@ -135,7 +135,7 @@ public void testCovarianceOfCompose3() {
         Observable<Movie> movie = Observable.<Movie>just(new HorrorMovie());
         Observable<HorrorMovie> movie2 = movie.compose(new Transformer<Movie, HorrorMovie>() {
             @Override
-            public Observable<? extends HorrorMovie> call(Observable<Movie> t1) {
+            public Observable<HorrorMovie> call(Observable<Movie> t1) {
                 return Observable.just(new HorrorMovie()).map(new Func1<HorrorMovie, HorrorMovie>() {
 
                     @Override
@@ -152,7 +152,7 @@ public void testCovarianceOfCompose4() {
         Observable<HorrorMovie> movie = Observable.just(new HorrorMovie());
         Observable<HorrorMovie> movie2 = movie.compose(new Transformer<HorrorMovie, HorrorMovie>() {
             @Override
-            public Observable<? extends HorrorMovie> call(Observable<HorrorMovie> t1) {
+            public Observable<HorrorMovie> call(Observable<HorrorMovie> t1) {
                 return t1.map(new Func1<HorrorMovie, HorrorMovie>() {
 
                     @Override