Widen types in signatures of Future companion methods, refactor OnceCanBuildFrom.

Removed the implicit modifier on the OnceCanBuildFrom, as we don't
support implicit classes with zero arguments.

Added an implicit OnceCanBuildFrom method.

The idea behind OnceCanBuildFrom is for it to be used by methods which
construct collections, but are defined outside of collection classes.
OnceCanBuildFrom so far worked only for objects of type TraversableOnce:

    shuffle(List(1, 2, 3).iterator: TraversableOnce[Int])

but this used to result in an implicit resolution error:

    shuffle(List(1, 2, 3).iterator)

because after the type parameter M for `shuffle` was inferred to Iterator, no implicit
of type CanBuildFrom[Iterator[_], A, Iterator[A]] could be found.

Introduced another CanBuildFrom to the Iterator companion object.

Modified Future tests appropriately.

Author: Aleksandar Prokopec

src/library/scala/collection/Iterator.scala

@@ -21,6 +21,14 @@ import immutable.Stream
  */
 object Iterator {
 
+  /** With the advent of `TraversableOnce` and `Iterator`, it can be useful to have a builder which
+   *  operates on `Iterator`s so they can be treated uniformly along with the collections.
+   *  See `scala.util.Random.shuffle` for an example.
+   */
+  implicit def IteratorCanBuildFrom[A] = new TraversableOnce.BufferedCanBuildFrom[A, Iterator] {
+    def toColl[B](coll: ArrayBuffer[B]) = coll.iterator
+  }
+
   /** The iterator which produces no values. */
   val empty: Iterator[Nothing] = new AbstractIterator[Nothing] {
     def hasNext: Boolean = false

src/library/scala/collection/TraversableOnce.scala

@@ -8,7 +8,7 @@
 
 package scala.collection
 
-import mutable.{ Buffer, ListBuffer, ArrayBuffer }
+import mutable.{ Buffer, Builder, ListBuffer, ArrayBuffer }
 import annotation.unchecked.{ uncheckedVariance => uV }
 import language.{implicitConversions, higherKinds}
 
@@ -357,7 +357,6 @@ trait TraversableOnce[+A] extends Any with GenTraversableOnce[A] {
 }
 
 
-
 object TraversableOnce {
   @deprecated("use OnceCanBuildFrom instead")
   def traversableOnceCanBuildFrom[T] = new OnceCanBuildFrom[T]
@@ -367,26 +366,34 @@ object TraversableOnce {
   implicit def alternateImplicit[A](trav: TraversableOnce[A]) = new ForceImplicitAmbiguity
   implicit def flattenTraversableOnce[A, CC[_]](travs: TraversableOnce[CC[A]])(implicit ev: CC[A] => TraversableOnce[A]) =
     new FlattenOps[A](travs map ev)
-
-  /** With the advent of TraversableOnce, it can be useful to have a builder which
-   *  operates on Iterators so they can be treated uniformly along with the collections.
-   *  See scala.util.Random.shuffle for an example.
-   */
-  implicit class OnceCanBuildFrom[A] extends generic.CanBuildFrom[TraversableOnce[A], A, TraversableOnce[A]] {
-    def newIterator = new ArrayBuffer[A] mapResult (_.iterator)
+  
+  abstract class BufferedCanBuildFrom[A, Coll[X] <: TraversableOnce[X]] extends generic.CanBuildFrom[Coll[_], A, Coll[A]] {
+    def toColl[B](buff: ArrayBuffer[B]): Coll[B]
+    
+    def newIterator: Builder[A, Coll[A]] = new ArrayBuffer[A] mapResult toColl
 
     /** Creates a new builder on request of a collection.
      *  @param from  the collection requesting the builder to be created.
      *  @return the result of invoking the `genericBuilder` method on `from`.
      */
-    def apply(from: TraversableOnce[A]) = newIterator
+    def apply(from: Coll[_]): Builder[A, Coll[A]] = newIterator
 
     /** Creates a new builder from scratch
      *  @return the result of invoking the `newBuilder` method of this factory.
      */
     def apply() = newIterator
   }
-
+  
+  /** With the advent of `TraversableOnce`, it can be useful to have a builder which
+   *  operates on `Iterator`s so they can be treated uniformly along with the collections.
+   *  See `scala.util.Random.shuffle` or `scala.concurrent.Future.sequence` for an example.
+   */
+  class OnceCanBuildFrom[A] extends BufferedCanBuildFrom[A, TraversableOnce] {
+    def toColl[B](buff: ArrayBuffer[B]) = buff.iterator
+  }
+  
+  implicit def OnceCanBuildFrom[A] = new OnceCanBuildFrom[A]
+  
   class FlattenOps[A](travs: TraversableOnce[TraversableOnce[A]]) {
     def flatten: Iterator[A] = new AbstractIterator[A] {
       val its = travs.toIterator

src/library/scala/concurrent/Future.scala

@@ -426,21 +426,8 @@ trait Future[+T] extends Awaitable[T] {
    *  that conforms to `S`'s erased type or a `ClassCastException` otherwise.
    */
   def mapTo[S](implicit tag: ClassTag[S]): Future[S] = {
-    import java.{ lang => jl }
-    val toBoxed = Map[Class[_], Class[_]](
-      classOf[Boolean] -> classOf[jl.Boolean],
-      classOf[Byte]    -> classOf[jl.Byte],
-      classOf[Char]    -> classOf[jl.Character],
-      classOf[Short]   -> classOf[jl.Short],
-      classOf[Int]     -> classOf[jl.Integer],
-      classOf[Long]    -> classOf[jl.Long],
-      classOf[Float]   -> classOf[jl.Float],
-      classOf[Double]  -> classOf[jl.Double],
-      classOf[Unit]    -> classOf[scala.runtime.BoxedUnit]
-    )
-
     def boxedType(c: Class[_]): Class[_] = {
-      if (c.isPrimitive) toBoxed(c) else c
+      if (c.isPrimitive) Future.toBoxed(c) else c
     }
 
     val p = newPromise[S]
@@ -530,7 +517,22 @@ trait Future[+T] extends Awaitable[T] {
  *  Note: using this method yields nondeterministic dataflow programs.
  */
 object Future {
- /** Starts an asynchronous computation and returns a `Future` object with the result of that computation.
+  
+  import java.{ lang => jl }
+  
+  private[concurrent] val toBoxed = Map[Class[_], Class[_]](
+    classOf[Boolean] -> classOf[jl.Boolean],
+    classOf[Byte]    -> classOf[jl.Byte],
+    classOf[Char]    -> classOf[jl.Character],
+    classOf[Short]   -> classOf[jl.Short],
+    classOf[Int]     -> classOf[jl.Integer],
+    classOf[Long]    -> classOf[jl.Long],
+    classOf[Float]   -> classOf[jl.Float],
+    classOf[Double]  -> classOf[jl.Double],
+    classOf[Unit]    -> classOf[scala.runtime.BoxedUnit]
+  )
+  
+  /** Starts an asynchronous computation and returns a `Future` object with the result of that computation.
   *
   *  The result becomes available once the asynchronous computation is completed.
   *
@@ -544,18 +546,18 @@ object Future {
   import scala.collection.mutable.Builder
   import scala.collection.generic.CanBuildFrom
 
-  /** Simple version of `Futures.traverse`. Transforms a `Traversable[Future[A]]` into a `Future[Traversable[A]]`.
+  /** Simple version of `Futures.traverse`. Transforms a `TraversableOnce[Future[A]]` into a `Future[TraversableOnce[A]]`.
    *  Useful for reducing many `Future`s into a single `Future`.
    */
-  def sequence[A, M[_] <: Traversable[_]](in: M[Future[A]])(implicit cbf: CanBuildFrom[M[Future[A]], A, M[A]], executor: ExecutionContext): Future[M[A]] = {
+  def sequence[A, M[_] <: TraversableOnce[_]](in: M[Future[A]])(implicit cbf: CanBuildFrom[M[Future[A]], A, M[A]], executor: ExecutionContext): Future[M[A]] = {
     in.foldLeft(Promise.successful(cbf(in)).future) {
       (fr, fa) => for (r <- fr; a <- fa.asInstanceOf[Future[A]]) yield (r += a)
     } map (_.result)
   }
 
   /** Returns a `Future` to the result of the first future in the list that is completed.
    */
-  def firstCompletedOf[T](futures: Traversable[Future[T]])(implicit executor: ExecutionContext): Future[T] = {
+  def firstCompletedOf[T](futures: TraversableOnce[Future[T]])(implicit executor: ExecutionContext): Future[T] = {
     val p = Promise[T]()
 
     val completeFirst: Either[Throwable, T] => Unit = p tryComplete _
@@ -566,7 +568,8 @@ object Future {
 
   /** Returns a `Future` that will hold the optional result of the first `Future` with a result that matches the predicate.
    */
-  def find[T](futures: Traversable[Future[T]])(predicate: T => Boolean)(implicit executor: ExecutionContext): Future[Option[T]] = {
+  def find[T](futurestravonce: TraversableOnce[Future[T]])(predicate: T => Boolean)(implicit executor: ExecutionContext): Future[Option[T]] = {
+    val futures = futurestravonce.toBuffer
     if (futures.isEmpty) Promise.successful[Option[T]](None).future
     else {
       val result = Promise[Option[T]]()
@@ -577,8 +580,9 @@ object Future {
           case _        =>
         }
       } finally {
-        if (ref.decrementAndGet == 0)
+        if (ref.decrementAndGet == 0) {
           result tryComplete Right(None)
+        }
       }
 
       futures.foreach(_ onComplete search)
@@ -597,7 +601,7 @@ object Future {
    *    val result = Await.result(Future.fold(futures)(0)(_ + _), 5 seconds)
    *  }}}
    */
-  def fold[T, R](futures: Traversable[Future[T]])(zero: R)(foldFun: (R, T) => R)(implicit executor: ExecutionContext): Future[R] = {
+  def fold[T, R](futures: TraversableOnce[Future[T]])(zero: R)(foldFun: (R, T) => R)(implicit executor: ExecutionContext): Future[R] = {
     if (futures.isEmpty) Promise.successful(zero).future
     else sequence(futures).map(_.foldLeft(zero)(foldFun))
   }
@@ -609,20 +613,20 @@ object Future {
    *    val result = Await.result(Futures.reduce(futures)(_ + _), 5 seconds)
    *  }}}
    */
-  def reduce[T, R >: T](futures: Traversable[Future[T]])(op: (R, T) => R)(implicit executor: ExecutionContext): Future[R] = {
+  def reduce[T, R >: T](futures: TraversableOnce[Future[T]])(op: (R, T) => R)(implicit executor: ExecutionContext): Future[R] = {
     if (futures.isEmpty) Promise[R].failure(new NoSuchElementException("reduce attempted on empty collection")).future
     else sequence(futures).map(_ reduceLeft op)
   }
 
-  /** Transforms a `Traversable[A]` into a `Future[Traversable[B]]` using the provided function `A => Future[B]`.
+  /** Transforms a `TraversableOnce[A]` into a `Future[TraversableOnce[B]]` using the provided function `A => Future[B]`.
    *  This is useful for performing a parallel map. For example, to apply a function to all items of a list
    *  in parallel:
    *
    *  {{{
    *    val myFutureList = Future.traverse(myList)(x => Future(myFunc(x)))
    *  }}}
    */
-  def traverse[A, B, M[_] <: Traversable[_]](in: M[A])(fn: A => Future[B])(implicit cbf: CanBuildFrom[M[A], B, M[B]], executor: ExecutionContext): Future[M[B]] =
+  def traverse[A, B, M[_] <: TraversableOnce[_]](in: M[A])(fn: A => Future[B])(implicit cbf: CanBuildFrom[M[A], B, M[B]], executor: ExecutionContext): Future[M[B]] =
     in.foldLeft(Promise.successful(cbf(in)).future) { (fr, a) =>
       val fb = fn(a.asInstanceOf[A])
       for (r <- fr; b <- fb) yield (r += b)

src/library/scala/concurrent/util/Duration.scala

@@ -1,12 +1,16 @@
-/**
- * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
- */
+/*                     __                                               *\
+**     ________ ___   / /  ___     Scala API                            **
+**    / __/ __// _ | / /  / _ |    (c) 2003-2012, LAMP/EPFL             **
+**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
+** /____/\___/_/ |_/____/_/ | |                                         **
+**                          |/                                          **
+\*                                                                      */
 
 package scala.concurrent.util
 
 import java.util.concurrent.TimeUnit
 import TimeUnit._
-import java.lang.{ Double ⇒ JDouble }
+import java.lang.{ Double => JDouble }
 import language.implicitConversions
 
 case class Deadline private (time: Duration) {