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author | Aleksandar Prokopec <aleksandar@aleksandar-Latitude-E6500.(none)> | 2012-05-01 17:12:01 +0200 |
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committer | Aleksandar Prokopec <aleksandar@aleksandar-Latitude-E6500.(none)> | 2012-05-01 17:12:01 +0200 |
commit | 187817b7969aecfcec68dfc910c5a01e57d8edc4 (patch) | |
tree | d44619bc1340ec144855414b03dac72b044a217a /src | |
parent | 5f29da78e954d93e5bc8b878565de8c2a2abe561 (diff) | |
download | scala-187817b7969aecfcec68dfc910c5a01e57d8edc4.tar.gz scala-187817b7969aecfcec68dfc910c5a01e57d8edc4.tar.bz2 scala-187817b7969aecfcec68dfc910c5a01e57d8edc4.zip |
Refactor OnceCanBuildFrom to check the collection type.
The builder is now instantiated as an iterator builder only
if a generic builder cannot be found on the collection that
requested the builder.
Reason - we want this behaviour:
scala> scala.util.Random.shuffle(List(1, 2, 3): collection.TraversableOnce[Int])
res0: scala.collection.TraversableOnce[Int] = List(3, 1, 2)
instead of this one:
scala> scala.util.Random.shuffle(List(1, 2, 3): collection.TraversableOnce[Int])
res0: scala.collection.TraversableOnce[Int] = non-empty iterator
which may lead to nasty surprises.
Alternately, to avoid pattern-matching in OnceCanBuildFrom.apply, we
could mix in GenericTraversableTemplate-related functionaly into
TraversableOnce, but this may become too complicated.
Diffstat (limited to 'src')
-rw-r--r-- | src/library/scala/collection/Iterator.scala | 3 | ||||
-rw-r--r-- | src/library/scala/collection/TraversableOnce.scala | 19 |
2 files changed, 16 insertions, 6 deletions
diff --git a/src/library/scala/collection/Iterator.scala b/src/library/scala/collection/Iterator.scala index af83291a46..3b2a7c7820 100644 --- a/src/library/scala/collection/Iterator.scala +++ b/src/library/scala/collection/Iterator.scala @@ -26,7 +26,8 @@ object Iterator { * 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 + def bufferToColl[B](coll: ArrayBuffer[B]) = coll.iterator + def traversableToColl[B](t: GenTraversable[B]) = t.toIterator } /** The iterator which produces no values. */ diff --git a/src/library/scala/collection/TraversableOnce.scala b/src/library/scala/collection/TraversableOnce.scala index b34daed2be..0334322dbc 100644 --- a/src/library/scala/collection/TraversableOnce.scala +++ b/src/library/scala/collection/TraversableOnce.scala @@ -367,16 +367,23 @@ object TraversableOnce { implicit def flattenTraversableOnce[A, CC[_]](travs: TraversableOnce[CC[A]])(implicit ev: CC[A] => TraversableOnce[A]) = new FlattenOps[A](travs map ev) - abstract class BufferedCanBuildFrom[A, Coll[X] <: TraversableOnce[X]] extends generic.CanBuildFrom[Coll[_], A, Coll[A]] { - def toColl[B](buff: ArrayBuffer[B]): Coll[B] + /* Functionality reused in Iterator.CanBuildFrom */ + private[collection] abstract class BufferedCanBuildFrom[A, Coll[X] <: TraversableOnce[X]] extends generic.CanBuildFrom[Coll[_], A, Coll[A]] { + def bufferToColl[B](buff: ArrayBuffer[B]): Coll[B] + def traversableToColl[B](t: GenTraversable[B]): Coll[B] - def newIterator: Builder[A, Coll[A]] = new ArrayBuffer[A] mapResult toColl + def newIterator: Builder[A, Coll[A]] = new ArrayBuffer[A] mapResult bufferToColl /** 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: Coll[_]): Builder[A, Coll[A]] = newIterator + def apply(from: Coll[_]): Builder[A, Coll[A]] = from match { + case xs: generic.GenericTraversableTemplate[_, _] => xs.genericBuilder mapResult { + case res => traversableToColl(res.asInstanceOf[GenTraversable[A]]) + } + case _ => newIterator + } /** Creates a new builder from scratch * @return the result of invoking the `newBuilder` method of this factory. @@ -389,9 +396,11 @@ object TraversableOnce { * 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 + def bufferToColl[B](buff: ArrayBuffer[B]) = buff.iterator + def traversableToColl[B](t: GenTraversable[B]) = t.seq } + /** Evidence for building collections from `TraversableOnce` collections */ implicit def OnceCanBuildFrom[A] = new OnceCanBuildFrom[A] class FlattenOps[A](travs: TraversableOnce[TraversableOnce[A]]) { |