diff options
-rw-r--r-- | src/library/scala/collection/TraversableViewLike.scala | 21 | ||||
-rw-r--r-- | test/files/run/view-headoption.check | 28 | ||||
-rw-r--r-- | test/files/run/view-headoption.scala | 18 |
3 files changed, 67 insertions, 0 deletions
diff --git a/src/library/scala/collection/TraversableViewLike.scala b/src/library/scala/collection/TraversableViewLike.scala index 36fe6251df..03286fef67 100644 --- a/src/library/scala/collection/TraversableViewLike.scala +++ b/src/library/scala/collection/TraversableViewLike.scala @@ -82,6 +82,27 @@ trait TraversableViewLike[+A, trait Transformed[+B] extends TraversableView[B, Coll] with super.Transformed[B] { def foreach[U](f: B => U): Unit + // Methods whose standard implementations use "isEmpty" need to be rewritten + // for views, else they will end up traversing twice in a situation like: + // xs.view.flatMap(f).headOption + override def headOption: Option[B] = { + for (x <- this) + return Some(x) + + None + } + override def lastOption: Option[B] = { + // (Should be) better than allocating a Some for every element. + var empty = true + var result: B = null.asInstanceOf[B] + for (x <- this) { + empty = false + result = x + } + if (empty) None else Some(result) + } + + // XXX: As yet not dealt with, tail and init both call isEmpty. override def stringPrefix = self.stringPrefix override def toString = viewToString } diff --git a/test/files/run/view-headoption.check b/test/files/run/view-headoption.check new file mode 100644 index 0000000000..5c98b54b46 --- /dev/null +++ b/test/files/run/view-headoption.check @@ -0,0 +1,28 @@ +fail +success +f1: Some(5) +fail +success +f2: 5 +fail +success +fail +fail +success +fail +fail +fail +success +f3: Some(5) +fail +success +fail +success +fail +fail +success +fail +fail +fail +success +f4: 5 diff --git a/test/files/run/view-headoption.scala b/test/files/run/view-headoption.scala new file mode 100644 index 0000000000..659c7e6b82 --- /dev/null +++ b/test/files/run/view-headoption.scala @@ -0,0 +1,18 @@ +object Test { + val failer = () => { println("fail") ; None } + val succeeder = () => { println("success") ; Some(5) } + val fs = List(failer, succeeder, failer, failer, succeeder, failer, failer, failer, succeeder) + + def f0 = fs.view flatMap (f => f()) + def f1 = f0.headOption + def f2 = f0.head + def f3 = f0.lastOption + def f4 = f0.last + + def main(args: Array[String]): Unit = { + println("f1: " + f1) + println("f2: " + f2) + println("f3: " + f3) + println("f4: " + f4) + } +} |