2.x: Add Maybe.flatMapSingle

src/main/java/io/reactivex/Maybe.java

@@ -2551,6 +2551,28 @@ public final <R> Flowable<R> flatMapPublisher(Function<? super T, ? extends Publ
         return toFlowable().flatMap(mapper);
     }
 
+    /**
+     * Returns a {@link Single} based on applying a specified function to the item emitted by the
+     * source {@link Maybe}, where that function returns a {@link Single}.
+     * <p>
+     * <img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.flatMapSingle.png" alt="">
+     * <dl>
+     * <dt><b>Scheduler:</b></dt>
+     * <dd>{@code flatMapSingle} does not operate by default on a particular {@link Scheduler}.</dd>
+     * </dl>
+     *
+     * @param mapper
+     *            a function that, when applied to the item emitted by the source Maybe, returns a
+     *            Single
+     * @return the Single returned from {@code mapper} when applied to the item emitted by the source Maybe
+     * @see <a href="http://reactivex.io/documentation/operators/flatmap.html">ReactiveX operators documentation: FlatMap</a>
+     */
+    @SchedulerSupport(SchedulerSupport.NONE)
+    public final Single<T> flatMapSingle(final Function<? super T, ? extends SingleSource<T>> mapper) {
+        ObjectHelper.requireNonNull(mapper, "mapper is null");
+        return RxJavaPlugins.onAssembly(new MaybeFlatMapSingle<T>(this, mapper));
+    }
+
     /**
      * Returns a {@link Completable} that completes based on applying a specified function to the item emitted by the
      * source {@link Maybe}, where that function returns a {@link Completable}.
@@ -2564,7 +2586,7 @@ public final <R> Flowable<R> flatMapPublisher(Function<? super T, ? extends Publ
      * @param mapper
      *            a function that, when applied to the item emitted by the source Maybe, returns a
      *            Completable
-     * @return the Completable returned from {@code func} when applied to the item emitted by the source Maybe
+     * @return the Completable returned from {@code mapper} when applied to the item emitted by the source Maybe
      * @see <a href="http://reactivex.io/documentation/operators/flatmap.html">ReactiveX operators documentation: FlatMap</a>
      */
     @SchedulerSupport(SchedulerSupport.NONE)

src/main/java/io/reactivex/internal/operators/maybe/MaybeFlatMapSingle.java

@@ -0,0 +1,132 @@
+/**
+ * Copyright 2016 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 io.reactivex.internal.operators.maybe;
+
+import io.reactivex.MaybeObserver;
+import io.reactivex.MaybeSource;
+import io.reactivex.Single;
+import io.reactivex.SingleObserver;
+import io.reactivex.SingleSource;
+import io.reactivex.disposables.Disposable;
+import io.reactivex.exceptions.Exceptions;
+import io.reactivex.functions.Function;
+import io.reactivex.internal.disposables.DisposableHelper;
+import io.reactivex.internal.functions.ObjectHelper;
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * Maps the success value of the source MaybeSource into a Single.
+ * @param <T>
+ */
+public final class MaybeFlatMapSingle<T> extends Single<T> {
+
+    final MaybeSource<T> source;
+
+    final Function<? super T, ? extends SingleSource<T>> mapper;
+
+    public MaybeFlatMapSingle(MaybeSource<T> source, Function<? super T, ? extends SingleSource<T>> mapper) {
+        this.source = source;
+        this.mapper = mapper;
+    }
+
+    @Override
+    protected void subscribeActual(SingleObserver<? super T> s) {
+        FlatMapMaybeObserver<T> parent = new FlatMapMaybeObserver<T>(s, mapper);
+        s.onSubscribe(parent);
+        source.subscribe(parent);
+    }
+
+    static final class FlatMapMaybeObserver<T>
+    extends AtomicReference<Disposable>
+    implements MaybeObserver<T>, Disposable {
+
+        private static final long serialVersionUID = 4827726964688405508L;
+
+        final SingleObserver actual;
+
+        final Function<? super T, ? extends SingleSource<T>> mapper;
+
+        FlatMapMaybeObserver(SingleObserver actual, Function<? super T, ? extends SingleSource<T>> mapper) {
+            this.actual = actual;
+            this.mapper = mapper;
+        }
+
+        @Override
+        public void dispose() {
+            DisposableHelper.dispose(this);
+        }
+
+        @Override
+        public boolean isDisposed() {
+            return DisposableHelper.isDisposed(get());
+        }
+
+        @Override
+        public void onSubscribe(Disposable d) {
+            DisposableHelper.replace(this, d);
+        }
+
+        @Override
+        public void onSuccess(T value) {
+            SingleSource<T> ss;
+
+            try {
+                ss = ObjectHelper.requireNonNull(mapper.apply(value), "The mapper returned a null SingleSource");
+            } catch (Throwable ex) {
+                Exceptions.throwIfFatal(ex);
+                onError(ex);
+                return;
+            }
+
+            ss.subscribe(new FlatMapSingleObserver<T>(this, actual));
+        }
+
+        @Override
+        public void onError(Throwable e) {
+            actual.onError(e);
+        }
+
+        @Override
+        public void onComplete() {
+            // Ignored.
+        }
+    }
+
+    static final class FlatMapSingleObserver<T> implements SingleObserver<T> {
+
+        final AtomicReference<Disposable> parent;
+
+        final SingleObserver<? super T> actual;
+
+        FlatMapSingleObserver(AtomicReference<Disposable> parent, SingleObserver<? super T> actual) {
+            this.parent = parent;
+            this.actual = actual;
+        }
+
+        @Override
+        public void onSubscribe(final Disposable d) {
+            DisposableHelper.replace(parent, d);
+        }
+
+        @Override
+        public void onSuccess(final T value) {
+            actual.onSuccess(value);
+        }
+
+        @Override
+        public void onError(final Throwable e) {
+            actual.onError(e);
+        }
+    }
+}

src/test/java/io/reactivex/internal/operators/maybe/MaybeFlatMapSingleTest.java

@@ -0,0 +1,94 @@
+/**
+ * Copyright 2016 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 io.reactivex.internal.operators.maybe;
+
+import io.reactivex.Maybe;
+import io.reactivex.Single;
+import io.reactivex.SingleSource;
+import io.reactivex.functions.Function;
+import org.junit.Test;
+
+public class MaybeFlatMapSingleTest {
+    @Test(expected = NullPointerException.class)
+    public void flatMapSingleNull() {
+        Maybe.just(1)
+            .flatMapSingle(null);
+    }
+
+    @Test
+    public void flatMapSingleValue() {
+        Maybe.just(1).flatMapSingle(new Function<Integer, SingleSource<Integer>>() {
+            @Override public SingleSource<Integer> apply(final Integer integer) throws Exception {
+                if (integer == 1) {
+                    return Single.just(2);
+                }
+
+                return Single.just(1);
+            }
+        })
+            .test()
+            .assertResult(2);
+    }
+
+    @Test
+    public void flatMapSingleValueNull() {
+        Maybe.just(1).flatMapSingle(new Function<Integer, SingleSource<Integer>>() {
+            @Override public SingleSource<Integer> apply(final Integer integer) throws Exception {
+                return null;
+            }
+        })
+            .test()
+            .assertNoValues()
+            .assertError(NullPointerException.class)
+            .assertErrorMessage("The mapper returned a null SingleSource");
+    }
+
+    @Test
+    public void flatMapSingleValueErrorThrown() {
+        Maybe.just(1).flatMapSingle(new Function<Integer, SingleSource<Integer>>() {
+            @Override public SingleSource<Integer> apply(final Integer integer) throws Exception {
+                throw new RuntimeException("something went terribly wrong!");
+            }
+        })
+            .test()
+            .assertNoValues()
+            .assertError(RuntimeException.class)
+            .assertErrorMessage("something went terribly wrong!");
+    }
+
+    @Test
+    public void flatMapSingleError() {
+        RuntimeException exception = new RuntimeException("test");
+
+        Maybe.error(exception).flatMapSingle(new Function<Object, SingleSource<Object>>() {
+            @Override public SingleSource<Object> apply(final Object integer) throws Exception {
+                return Single.just(new Object());
+            }
+        })
+            .test()
+            .assertError(exception);
+    }
+
+    @Test
+    public void flatMapSingleEmpty() {
+        Maybe.<Integer>empty().flatMapSingle(new Function<Integer, SingleSource<Integer>>() {
+            @Override public SingleSource<Integer> apply(final Integer integer) throws Exception {
+                return Single.just(2);
+            }
+        })
+            .test()
+            .assertNoValues()
+            .assertNoErrors();
+    }
+}