Add flatMap variants to RxScala

Author: zsxwing

language-adaptors/rxjava-scala/src/examples/scala/rx/lang/scala/examples/RxScalaDemo.scala

@@ -1108,4 +1108,65 @@ class RxScalaDemo extends JUnitSuite {
     }
     o.toBlockingObservable.foreach(println(_))
   }
+
+  @Test def flatMapExample() {
+    val o = Observable.items(10, 100)
+    o.flatMap(n => Observable.interval(200 millis).map(_ * n))
+      .take(20)
+      .toBlocking.foreach(println)
+  }
+
+  @Test def flatMapExample2() {
+    val o = Observable.items(10, 100)
+    val o1 = for (n <- o;
+                  i <- Observable.interval(200 millis)) yield i * n
+    o1.take(20).toBlocking.foreach(println)
+  }
+
+  @Test def flatMapExample3() {
+    val o = Observable[Int] {
+      subscriber =>
+        subscriber.onNext(10)
+        subscriber.onNext(100)
+        subscriber.onError(new IOException("Oops"))
+    }
+    o.flatMap(
+      (n: Int) => Observable.interval(200 millis).map(_ * n),
+      e => Observable.interval(200 millis).map(_ * -1),
+      () => Observable.interval(200 millis).map(_ * 1000)
+    ).take(20)
+      .toBlocking.foreach(println)
+  }
+
+  @Test def flatMapExample4() {
+    val o = Observable.items(10, 100)
+    o.flatMap(
+      (n: Int) => Observable.interval(200 millis).map(_ * n),
+      e => Observable.interval(200 millis).map(_ * -1),
+      () => Observable.interval(200 millis).map(_ * 1000)
+    ).take(20)
+      .toBlocking.foreach(println)
+  }
+
+  @Test def flatMapExample5() {
+    val o = Observable.items(1, 10, 100, 1000)
+    o.flatMap(
+      (n: Int) => Observable.interval(200 millis).take(5),
+      (n: Int, m: Long) => n * m
+    ).toBlocking.foreach(println)
+  }
+
+  @Test def flatMapIterableExample() {
+    val o = Observable.items(10, 100)
+    o.flatMapIterable(n => (1 to 20).map(_ * n))
+      .toBlocking.foreach(println)
+  }
+
+  @Test def flatMapIterableExample2() {
+    val o = Observable.items(1, 10, 100, 1000)
+    o.flatMapIterable(
+      (n: Int) => (1 to 5),
+      (n: Int, m: Int) => n * m
+    ).toBlocking.foreach(println)
+  }
 }

language-adaptors/rxjava-scala/src/main/scala/rx/lang/scala/Observable.scala

@@ -883,6 +883,95 @@ trait Observable[+T]
     }))
   }
 
+  /**
+   * Returns an Observable that applies a function to each item emitted or notification raised by the source
+   * Observable and then flattens the Observables returned from these functions and emits the resulting items.
+   *
+   * <img width="640" height="410" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/mergeMap.nce.png">
+   *
+   * @tparam R the result type
+   * @param onNext a function that returns an Observable to merge for each item emitted by the source Observable
+   * @param onError a function that returns an Observable to merge for an onError notification from the source
+   *                Observable
+   * @param onCompleted a function that returns an Observable to merge for an onCompleted notification from the source
+   *                    Observable
+   * @return an Observable that emits the results of merging the Observables returned from applying the
+   *         specified functions to the emissions and notifications of the source Observable
+   */
+  def flatMap[R](onNext: T => Observable[R], onError: Throwable => Observable[R], onCompleted: () => Observable[R]): Observable[R] = {
+    val jOnNext = new Func1[T, rx.Observable[_ <: R]] {
+      override def call(t: T): rx.Observable[_ <: R] = onNext(t).asJavaObservable
+    }
+    val jOnError = new Func1[Throwable, rx.Observable[_ <: R]] {
+      override def call(e: Throwable): rx.Observable[_ <: R] = onError(e).asJavaObservable
+    }
+    val jOnCompleted = new Func0[rx.Observable[_ <: R]] {
+      override def call(): rx.Observable[_ <: R] = onCompleted().asJavaObservable
+    }
+    toScalaObservable[R](asJavaObservable.mergeMap[R](jOnNext, jOnError, jOnCompleted))
+  }
+
+  /**
+   * Returns an Observable that emits the results of a specified function to the pair of values emitted by the
+   * source Observable and a specified collection Observable.
+   *
+   * <img width="640" height="390" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/mergeMap.r.png">
+   *
+   * @tparam U the type of items emitted by the collection Observable
+   * @tparam R the type of items emitted by the resulting Observable
+   * @param collectionSelector a function that returns an Observable for each item emitted by the source Observable
+   * @param resultSelector a function that combines one item emitted by each of the source and collection Observables and
+   *                       returns an item to be emitted by the resulting Observable
+   * @return an Observable that emits the results of applying a function to a pair of values emitted by the
+   *         source Observable and the collection Observable
+   */
+  def flatMap[U, R](collectionSelector: T => Observable[U], resultSelector: (T, U) => R): Observable[R] = {
+    val jCollectionSelector = new Func1[T, rx.Observable[_ <: U]] {
+      override def call(t: T): rx.Observable[_ <: U] = collectionSelector(t).asJavaObservable
+    }
+    toScalaObservable[R](asJavaObservable.mergeMap[U, R](jCollectionSelector, resultSelector))
+  }
+
+  /**
+   * Returns an Observable that merges each item emitted by the source Observable with the values in an
+   * Iterable corresponding to that item that is generated by a selector.
+   *
+   * <img width="640" height="310" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/mergeMapIterable.png">
+   *
+   * @tparam R the type of item emitted by the resulting Observable
+   * @param collectionSelector a function that returns an Iterable sequence of values for when given an item emitted by the
+   *                           source Observable
+   * @return an Observable that emits the results of merging the items emitted by the source Observable with
+   *         the values in the Iterables corresponding to those items, as generated by `collectionSelector
+   */
+  def flatMapIterable[R](collectionSelector: T => Iterable[R]): Observable[R] = {
+    val jCollectionSelector = new Func1[T, java.lang.Iterable[_ <: R]] {
+      override def call(t: T): java.lang.Iterable[_ <: R] = collectionSelector(t).asJava
+    }
+    toScalaObservable[R](asJavaObservable.mergeMapIterable[R](jCollectionSelector))
+  }
+
+  /**
+   * Returns an Observable that emits the results of applying a function to the pair of values from the source
+   * Observable and an Iterable corresponding to that item that is generated by a selector.
+   *
+   * <img width="640" height="390" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/mergeMapIterable.r.png">
+   *
+   * @tparam U the collection element type
+   * @tparam R the type of item emited by the resulting Observable
+   * @param collectionSelector a function that returns an Iterable sequence of values for each item emitted by the source
+   *                           Observable
+   * @param resultSelector a function that returns an item based on the item emitted by the source Observable and the
+   *                       Iterable returned for that item by the `collectionSelector`
+   * @return an Observable that emits the items returned by `resultSelector` for each item in the source Observable
+   */
+  def flatMapIterable[U, R](collectionSelector: T => Iterable[U], resultSelector: (T, U) => R): Observable[R] = {
+    val jCollectionSelector = new Func1[T, java.lang.Iterable[_ <: U]] {
+      override def call(t: T): java.lang.Iterable[_ <: U] = collectionSelector(t).asJava
+    }
+    toScalaObservable[R](asJavaObservable.mergeMapIterable[U, R](jCollectionSelector, resultSelector))
+  }
+
   /**
    * Returns an Observable that applies the given function to each item emitted by an
    * Observable and emits the result.

language-adaptors/rxjava-scala/src/test/scala/rx/lang/scala/CompletenessTest.scala

@@ -95,6 +95,11 @@ class CompletenessTest extends JUnitSuite {
       "lift(Operator[_ <: R, _ >: T])" -> "lift(Subscriber[R] => Subscriber[T])",
       "limit(Int)" -> "take(Int)",
       "mapWithIndex(Func2[_ >: T, Integer, _ <: R])" -> "[combine `zipWithIndex` with `map` or with a for comprehension]",
+      "mergeMap(Func1[_ >: T, _ <: Observable[_ <: R]])" -> "flatMap(T => Observable[R])",
+      "mergeMap(Func1[_ >: T, _ <: Observable[_ <: R]], Func1[_ >: Throwable, _ <: Observable[_ <: R]], Func0[_ <: Observable[_ <: R]])" -> "flatMap(T => Observable[R], Throwable => Observable[R], () => Observable[R])",
+      "mergeMap(Func1[_ >: T, _ <: Observable[_ <: U]], Func2[_ >: T, _ >: U, _ <: R])" -> "flatMap(T => Observable[U], (T, U) => R)",
+      "mergeMapIterable(Func1[_ >: T, _ <: Iterable[_ <: R]])" -> "flatMapIterable(T => Iterable[R])",
+      "mergeMapIterable(Func1[_ >: T, _ <: Iterable[_ <: U]], Func2[_ >: T, _ >: U, _ <: R])" -> "flatMapIterable(T => Iterable[U], (T, U) => R)",
       "multicast(Subject[_ >: T, _ <: R])" -> "multicast(Subject[R])",
       "multicast(Func0[_ <: Subject[_ >: T, _ <: TIntermediate]], Func1[_ >: Observable[TIntermediate], _ <: Observable[TResult]])" -> "multicast(() => Subject[R], Observable[R] => Observable[U])",
       "onErrorResumeNext(Func1[Throwable, _ <: Observable[_ <: T]])" -> "onErrorResumeNext(Throwable => Observable[U])",