RxScala: Add more operators to match RxJava

Author: zsxwing

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

@@ -379,6 +379,18 @@ class RxScalaDemo extends JUnitSuite {
     waitFor(Olympics.yearTicks)
   }
 
+  @Test def groupByExample2() {
+    val medalByYear = Olympics.mountainBikeMedals.groupBy(medal => medal.year, medal => medal.country)
+
+    for ((year, countries) <- medalByYear; country <- countries) {
+      println(s"${year}: ${country}")
+    }
+
+    Olympics.yearTicks.subscribe(year => println(s"\nYear $year starts."))
+
+    waitFor(Olympics.yearTicks)
+  }
+
   @Test def groupByUntilExample() {
     val numbers = Observable.interval(250 millis).take(14)
     val grouped = numbers.groupByUntil(x => x % 2){ case (key, obs) => obs.filter(x => x == 7) }
@@ -1510,4 +1522,104 @@ class RxScalaDemo extends JUnitSuite {
     o.take(3).toBlocking.foreach(println)
   }
 
+  @Test def collectExample() {
+    val o = Observable.just(1, 1.0, "a", 2, 2.0, "b")
+    o.collect { case s: String => "Item: " + s }.foreach(println(_))
+  }
+
+  @Test def usingExample() {
+    import scala.io.{Codec, Source}
+
+    Observable.using { new java.net.URL("http://rxscala.github.io/").openStream() }(
+      input => Source.fromInputStream(input)(Codec.UTF8).getLines().toList.toObservable,
+      input => input.close
+    ).foreach(println(_))
+  }
+
+  def createFastObservable: Observable[Int] = {
+    Observable {
+      subscriber: Subscriber[Int] => {
+        (0 to 2000).takeWhile(_ => !subscriber.isUnsubscribed).foreach(subscriber.onNext(_))
+        subscriber.onCompleted()
+      }
+    }
+  }
+
+  @Test def withoutBackpressureExample() {
+    val o = createFastObservable
+    val l = new CountDownLatch(1)
+    o.observeOn(NewThreadScheduler()).subscribe(new Subscriber[Int] {
+      override def onStart() {
+        request(1)
+      }
+
+      override def onNext(n: Int) {
+        println(n)
+        Thread.sleep(10) // emulate a slow subscriber
+        request(1)
+      }
+
+      override def onError(e: Throwable) {
+        e.printStackTrace()
+        l.countDown()
+      }
+
+      override def onCompleted() {
+        l.countDown()
+      }
+    })
+    l.await()
+  }
+
+  @Test def onBackpressureDropExample() {
+    val o = createFastObservable.onBackpressureDrop
+    val l = new CountDownLatch(1)
+    o.observeOn(NewThreadScheduler()).subscribe(new Subscriber[Int] {
+      override def onStart() {
+        request(1)
+      }
+
+      override def onNext(n: Int) {
+        println(n)
+        Thread.sleep(10) // emulate a slow subscriber
+        request(1)
+      }
+
+      override def onError(e: Throwable) {
+        e.printStackTrace()
+        l.countDown()
+      }
+
+      override def onCompleted() {
+        l.countDown()
+      }
+    })
+    l.await()
+  }
+
+  @Test def onBackpressureBufferExample() {
+    val o = createFastObservable.onBackpressureBuffer
+    val l = new CountDownLatch(1)
+    o.observeOn(NewThreadScheduler()).subscribe(new Subscriber[Int] {
+      override def onStart() {
+        request(1)
+      }
+
+      override def onNext(n: Int) {
+        println(n)
+        Thread.sleep(10) // emulate a slow subscriber
+        request(1)
+      }
+
+      override def onError(e: Throwable) {
+        e.printStackTrace()
+        l.countDown()
+      }
+
+      override def onCompleted() {
+        l.countDown()
+      }
+    })
+    l.await()
+  }
 }

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

@@ -62,4 +62,12 @@ object JavaConversions {
       }
     }
   }
+
+  implicit def toJavaTransformer[T, R](transformer: Observable[T] => Observable[R]): rx.Observable.Transformer[T, R] = {
+    new rx.Observable.Transformer[T, R] {
+      override def call(o: rx.Observable[_ <: T]): rx.Observable[R] = {
+        transformer(toScalaObservable(o)).asJavaObservable.asInstanceOf[rx.Observable[R]]
+      }
+    }
+  }
 }

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

@@ -864,6 +864,38 @@ trait Observable[+T]
       : Observable[Observable[T]] // SI-7818
   }
 
+  /**
+   * Returns an Observable that emits windows of items it collects from the source Observable. The resulting
+   * Observable starts a new window periodically, as determined by the `timeshift` argument or a maximum
+   * size as specified by the `count` argument (whichever is reached first). It emits
+   * each window after a fixed timespan, specified by the `timespan` argument. When the source
+   * Observable completes or Observable completes or encounters an error, the resulting Observable emits the
+   * current window and propagates the notification from the source Observable.
+   *
+   * <img width="640" height="335" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/window7.s.png" alt="">
+   *
+   * ===Backpressure Support:===
+   * This operator does not support backpressure as it uses time to control data flow.
+   *
+   * ===Scheduler:===
+   * you specify which `Scheduler` this operator will use
+   *
+   * @param timespan the period of time each window collects items before it should be emitted
+   * @param timeshift the period of time after which a new window will be created
+   * @param count the maximum size of each window before it should be emitted
+   * @param scheduler the `Scheduler` to use when determining the end and start of a window
+   * @return an Observable that emits new windows periodically as a fixed timespan elapses
+   * @see <a href="https://github.com/Netflix/RxJava/wiki/Transforming-Observables#window">RxJava wiki: window</a>
+   * @see <a href="http://msdn.microsoft.com/en-us/library/system.reactive.linq.observable.window.aspx">MSDN: Observable.Window</a>
+   */
+  def sliding(timespan: Duration, timeshift: Duration, count: Int, scheduler: Scheduler): Observable[Observable[T]] = {
+    val span: Long = timespan.length
+    val shift: Long = timespan.unit.convert(timeshift.length, timeshift.unit)
+    val unit: TimeUnit = timespan.unit
+    Observable.jObsOfJObsToScObsOfScObs(asJavaObservable.window(span, shift, unit, count, scheduler))
+      : Observable[Observable[T]] // SI-7818
+  }
+
   /**
    * Returns an Observable which only emits those items for which a given predicate holds.
    *
@@ -1577,6 +1609,41 @@ trait Observable[+T]
     toScalaObservable[T](asJavaObservable.cache())
   }
 
+  /**
+   * Caches emissions from the source Observable and replays them in order to any subsequent Subscribers.
+   * This method has similar behavior to [[Observable.replay]] except that this auto-subscribes to the source
+   * Observable rather than returning a [[ConnectableObservable]] for which you must call
+   * `connect` to activate the subscription.
+   * <p>
+   * <img width="640" height="410" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/cache.png" alt="">
+   * <p>
+   * This is useful when you want an Observable to cache responses and you can't control the
+   * `subscribe/unsubscribe` behavior of all the [[Subscriber]]s.
+   * <p>
+   * When you call `cache`, it does not yet subscribe to the source Observable and so does not yet
+   * begin cacheing items. This only happens when the first Subscriber calls the resulting Observable's
+   * `subscribe` method.
+   * <p>
+   * <em>Note:</em> You sacrifice the ability to unsubscribe from the origin when you use the `cache`
+   * Observer so be careful not to use this Observer on Observables that emit an infinite or very large number
+   * of items that will use up memory.
+   *
+   * ===Backpressure Support:===
+   * This operator does not support upstream backpressure as it is purposefully requesting and caching everything emitted.
+   *
+   * ===Scheduler:===
+   * `cache` does not operate by default on a particular `Scheduler`.
+   *
+   * @param capacity hint for number of items to cache (for optimizing underlying data structure)
+   * @return an Observable that, when first subscribed to, caches all of its items and notifications for the
+   *         benefit of subsequent subscribers
+   * @see <a href="https://github.com/Netflix/RxJava/wiki/Observable-Utility-Operators#cache">RxJava wiki: cache</a>
+   * @since 0.20
+   */
+  def cache(capacity: Int): Observable[T] = {
+    toScalaObservable[T](asJavaObservable.cache(capacity))
+  }
+
   /**
    * Returns a new [[Observable]] that multicasts (shares) the original [[Observable]]. As long a
    * there is more than 1 [[Subscriber]], this [[Observable]] will be subscribed and emitting data.
@@ -2176,6 +2243,41 @@ trait Observable[+T]
     toScalaObservable[(K, Observable[T])](o1.map[(K, Observable[T])](func))
   }
 
+  /**
+   * Groups the items emitted by an [[Observable]] according to a specified criterion, and emits these
+   * grouped items as `(key, observable)` pairs.
+   *
+   * <img width="640" height="360" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/groupBy.png" alt="">
+   *
+   * Note: A `(key, observable)` will cache the items it is to emit until such time as it
+   * is subscribed to. For this reason, in order to avoid memory leaks, you should not simply ignore those
+   * `(key, observable)` pairs that do not concern you. Instead, you can signal to them that they may
+   * discard their buffers by applying an operator like `take(0)` to them.
+   *
+   * ===Backpressure Support:===
+   * This operator does not support backpressure as splitting a stream effectively turns it into a "hot observable"
+   * and blocking any one group would block the entire parent stream. If you need backpressure on individual groups
+   * then you should use operators such as `nBackpressureDrop` or `@link #onBackpressureBuffer`.</dd>
+   * ===Scheduler:===
+   * groupBy` does not operate by default on a particular `Scheduler`.
+   *
+   * @param keySelector a function that extracts the key for each item
+   * @param valueSelector a function that extracts the return element for each item
+   * @tparam K the key type
+   * @tparam V the value type
+   * @return an [[Observable]] that emits `(key, observable)` pairs, each of which corresponds to a
+   *         unique key value and each of which emits those items from the source Observable that share that
+   *         key value
+   * @see <a href="https://github.com/Netflix/RxJava/wiki/Transforming-Observables#groupby-and-groupbyuntil">RxJava wiki: groupBy</a>
+   * @see <a href="http://msdn.microsoft.com/en-us/library/system.reactive.linq.observable.groupby.aspx">MSDN: Observable.GroupBy</a>
+   */
+  def groupBy[K, V](keySelector: T => K, valueSelector: T => V): Observable[(K, Observable[V])] = {
+    val jo: rx.Observable[rx.observables.GroupedObservable[K, V]] = asJavaObservable.groupBy[K, V](keySelector, valueSelector)
+    toScalaObservable[rx.observables.GroupedObservable[K, V]](jo).map {
+      go: rx.observables.GroupedObservable[K, V] => (go.getKey, toScalaObservable[V](go))
+    }
+  }
+
   /**
    * Groups the items emitted by this Observable according to a specified discriminator function and terminates these groups
    * according to a function.
@@ -4298,6 +4400,75 @@ trait Observable[+T]
   def nonEmpty: Observable[Boolean] = {
     isEmpty.map(!_)
   }
+
+  /**
+   * Transform an Observable by applying a particular Transformer function to it.
+   *
+   * This method operates on the Observable itself whereas [[Observable.lift]] operates on the Observable's
+   * Subscribers or Observers.
+   *
+   * If the operator you are creating is designed to act on the individual items emitted by a source
+   * Observable, use [[Observable.lift]]. If your operator is designed to transform the source Observable as a whole
+   * (for instance, by applying a particular set of existing RxJava operators to it) use `compose`.
+   *
+   * ===Scheduler:===
+   * `compose` does not operate by default on a particular [[Scheduler]].
+   *
+   * @param transformer implements the function that transforms the source Observable
+   * @return the source Observable, transformed by the transformer function
+   * @see <a href="https://github.com/Netflix/RxJava/wiki/Implementing-Your-Own-Operators">RxJava wiki: Implementing Your Own Operators</a>
+   */
+  def compose[R](transformer: Observable[T] => Observable[R]): Observable[R] = {
+    toScalaObservable[R](asJavaObservable.compose(toJavaTransformer(transformer)))
+  }
+
+  /**
+   * Instructs an Observable that is emitting items faster than its observer can consume them to buffer these
+   * items indefinitely until they can be emitted.
+   *
+   * <img width="640" height="300" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/bp.obp.buffer.png" alt="">
+   *
+   * ===Scheduler:===
+   * `onBackpressureBuffer` does not operate by default on a particular `Scheduler`.
+   *
+   * @return the source Observable modified to buffer items to the extent system resources allow
+   * @see <a href="https://github.com/Netflix/RxJava/wiki/Backpressure">RxJava wiki: Backpressure</a>
+   */
+  def onBackpressureBuffer: Observable[T] = {
+    toScalaObservable[T](asJavaObservable.onBackpressureBuffer)
+  }
+
+  /**
+   * Use this operator when the upstream does not natively support backpressure and you wish to drop
+   * `onNext` when unable to handle further events.
+   *
+   * <img width="640" height="245" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/bp.obp.drop.png" alt="">
+   *
+   * If the downstream request count hits 0 then `onNext` will be dropped until `request(long n)`
+   * is invoked again to increase the request count.
+   *
+   * ===Scheduler:===
+   * onBackpressureDrop` does not operate by default on a particular `Scheduler`.
+   *
+   * @return the source Observable modified to drop `onNext` notifications on overflow
+   * @see <a href="https://github.com/Netflix/RxJava/wiki/Backpressure">RxJava wiki: Backpressure</a>
+   */
+  def onBackpressureDrop: Observable[T] = {
+    toScalaObservable[T](asJavaObservable.onBackpressureDrop)
+  }
+
+  /**
+   * Return a new [[Observable]] by applying a partial function to all elements of this [[Observable]]
+   * on which the function is defined.
+   *
+   * @tparam R the element type of the returned [[Observable]].
+   * @param pf the partial function which filters and maps the [[Observable]].
+   * @return a new [[Observable]] by applying a partial function to all elements of this [[Observable]]
+   *         on which the function is defined.
+   */
+  def collect[R](pf: PartialFunction[T, R]): Observable[R] = {
+    filter(pf.isDefinedAt(_)).map(pf)
+  }
 }
 
 /**
@@ -4746,6 +4917,7 @@ object Observable {
    * @param observableFactory the factory function to obtain an Observable
    * @return the Observable whose lifetime controls the lifetime of the dependent resource object
    */
+  @deprecated("Use `using(=> Resource)(Resource => Observable[T], Resource => Unit)` instead", "0.20.1")
   def using[T, Resource <: Subscription](resourceFactory: () => Resource, observableFactory: Resource => Observable[T]): Observable[T] = {
     class ResourceSubscription(val resource: Resource) extends rx.Subscription {
       def unsubscribe = resource.unsubscribe
@@ -4759,6 +4931,32 @@ object Observable {
     ))
   }
 
+  /**
+   * Constructs an Observable that creates a dependent resource object.
+   *
+   * <img width="640" height="400" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/using.png" alt="" />
+   *
+   * ===Scheduler:===
+   * `using` does not operate by default on a particular `Scheduler`.
+   *
+   * @param resourceFactory the factory function to create a resource object that depends on the Observable.
+   *                        Note: this is a by-name parameter.
+   * @param observableFactory the factory function to create an Observable
+   * @param dispose the function that will dispose of the resource
+   * @return the Observable whose lifetime controls the lifetime of the dependent resource object
+   * @see <a href="https://github.com/Netflix/RxJava/wiki/Observable-Utility-Operators#using">RxJava wiki: using</a>
+   * @see <a href="http://msdn.microsoft.com/en-us/library/hh229585.aspx">MSDN: Observable.Using</a>
+   */
+  def using[T, Resource](resourceFactory: => Resource)(observableFactory: Resource => Observable[T], dispose: Resource => Unit): Observable[T] = {
+    val jResourceFactory = new rx.functions.Func0[Resource] {
+      override def call: Resource = resourceFactory
+    }
+    val jObservableFactory = new rx.functions.Func1[Resource, rx.Observable[_ <: T]] {
+      override def call(r: Resource) = observableFactory(r).asJavaObservable
+    }
+    toScalaObservable[T](rx.Observable.using[T, Resource](jResourceFactory, jObservableFactory, dispose))
+  }
+
   /**
    * Mirror the one Observable in an Iterable of several Observables that first emits an item.
    *

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

@@ -38,5 +38,7 @@ private[scala] class WithFilter[+T] (p: T => Boolean, asJava: rx.Observable[_ <:
     toScalaObservable[T](asJava.filter((x: T) => p(x) && q(x)))
   }
 
-  // there is no foreach here, that's only available on BlockingObservable
+  def foreach(onNext: T => Unit): Unit = {
+    toScalaObservable[T](asJava.filter(p)).foreach(onNext)
+  }
 }