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Diffstat (limited to 'src/library/scala/collection/mutable/Builder.scala')
| -rw-r--r-- | src/library/scala/collection/mutable/Builder.scala | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/src/library/scala/collection/mutable/Builder.scala b/src/library/scala/collection/mutable/Builder.scala index bbf4f5889d..b6887df61e 100644 --- a/src/library/scala/collection/mutable/Builder.scala +++ b/src/library/scala/collection/mutable/Builder.scala @@ -62,9 +62,27 @@ trait Builder[-Elem, +To] extends Growable[Elem] { * wrong, i.e. a different number of elements is added. * * @param coll the collection which serves as a hint for the result's size. + */ + def sizeHint(coll: TraversableLike[_, _]) { + if (coll.isInstanceOf[collection.IndexedSeqLike[_,_]]) { + sizeHint(coll.size) + } + } + + /** Gives a hint that one expects the `result` of this builder + * to have the same size as the given collection, plus some delta. This will + * provide a hint only if the collection is known to have a cheap + * `size` method. Currently this is assumed to be the case if and only if + * the collection is of type `IndexedSeqLike`. + * Some builder classes + * will optimize their representation based on the hint. However, + * builder implementations are still required to work correctly even if the hint is + * wrong, i.e. a different number of elements is added. + * + * @param coll the collection which serves as a hint for the result's size. * @param delta a correction to add to the `coll.size` to produce the size hint. */ - def sizeHint(coll: TraversableLike[_, _], delta: Int = 0) { + def sizeHint(coll: TraversableLike[_, _], delta: Int) { if (coll.isInstanceOf[collection.IndexedSeqLike[_,_]]) { sizeHint(coll.size + delta) } |