diff options
| -rw-r--r-- | src/library/scala/collection/Iterator.scala | 13 | ||||
| -rw-r--r-- | test/junit/scala/collection/IteratorTest.scala | 8 |
2 files changed, 15 insertions, 6 deletions
diff --git a/src/library/scala/collection/Iterator.scala b/src/library/scala/collection/Iterator.scala index e321a6adba..f6f46e158f 100644 --- a/src/library/scala/collection/Iterator.scala +++ b/src/library/scala/collection/Iterator.scala @@ -922,6 +922,9 @@ trait Iterator[+A] extends TraversableOnce[A] { /** For reasons which remain to be determined, calling * self.take(n).toSeq cause an infinite loop, so we have * a slight variation on take for local usage. + * NB: self.take.toSeq is slice.toStream, lazily built on self, + * so a subsequent self.hasNext would not test self after the + * group was consumed. */ private def takeDestructively(size: Int): Seq[A] = { val buf = new ArrayBuffer[A] @@ -945,12 +948,10 @@ trait Iterator[+A] extends TraversableOnce[A] { // so the rest of the code can be oblivious val xs: Seq[B] = { val res = takeDestructively(count) - // extra checks so we don't calculate length unless there's reason - if (pad.isDefined && !self.hasNext) { - val shortBy = count - res.length - if (shortBy > 0) res ++ padding(shortBy) else res - } - else res + // was: extra checks so we don't calculate length unless there's reason + // but since we took the group eagerly, just use the fast length + val shortBy = count - res.length + if (shortBy > 0 && pad.isDefined) res ++ padding(shortBy) else res } lazy val len = xs.length lazy val incomplete = len < count diff --git a/test/junit/scala/collection/IteratorTest.scala b/test/junit/scala/collection/IteratorTest.scala index cb7cbb40bc..b7a9805c9f 100644 --- a/test/junit/scala/collection/IteratorTest.scala +++ b/test/junit/scala/collection/IteratorTest.scala @@ -17,4 +17,12 @@ class IteratorTest { slidingIt.next assertEquals("Counter should be one, that means we didn't look further than needed", 1, counter) } + + @Test def groupedIteratorIsLazyWhenPadded(): Unit = { + var counter = 0 + def it = new Iterator[Int] { var i = 0 ; def hasNext = { counter = i; true } ; def next = { i += 1; i } } + val slidingIt = it sliding 2 withPadding -1 + slidingIt.next + assertEquals("Counter should be one, that means we didn't look further than needed", 1, counter) + } } |