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author | Rory Graves <rory.graves@fieldmark.co.uk> | 2016-10-17 20:25:31 +0100 |
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committer | Adriaan Moors <adriaan@lightbend.com> | 2017-01-28 14:02:44 -0800 |
commit | eb5c51383a63c5c3420e53ef021607ff5fd20296 (patch) | |
tree | a051a3957a2d8913346f924d943843a71ff77594 /src/library/scala/collection | |
parent | d540bf01fe4d9e5c56a68b0d3bada9d97af77e3f (diff) | |
download | scala-eb5c51383a63c5c3420e53ef021607ff5fd20296.tar.gz scala-eb5c51383a63c5c3420e53ef021607ff5fd20296.tar.bz2 scala-eb5c51383a63c5c3420e53ef021607ff5fd20296.zip |
Optimised implementation of List.filter/filterNot
Diffstat (limited to 'src/library/scala/collection')
-rw-r--r-- | src/library/scala/collection/immutable/FilteredTraversableInternal.scala | 104 | ||||
-rw-r--r-- | src/library/scala/collection/immutable/List.scala | 2 |
2 files changed, 106 insertions, 0 deletions
diff --git a/src/library/scala/collection/immutable/FilteredTraversableInternal.scala b/src/library/scala/collection/immutable/FilteredTraversableInternal.scala new file mode 100644 index 0000000000..35585b7826 --- /dev/null +++ b/src/library/scala/collection/immutable/FilteredTraversableInternal.scala @@ -0,0 +1,104 @@ +/* __ *\ +** ________ ___ / / ___ Scala API ** +** / __/ __// _ | / / / _ | (c) 2003-2013, LAMP/EPFL ** +** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ ** +** /____/\___/_/ |_/____/_/ | | ** +** |/ ** +\* */ + +package scala +package collection +package immutable + +import scala.annotation.tailrec + +/** + * Optimised filter functions for List + * n.b. this is an internal class to help maintain compatibility and should not be used directly. + */ +private[immutable] trait FilteredTraversableInternal[+A, +Repr <: AnyRef with TraversableLike[A, Repr]] extends TraversableLike[A, Repr] { + + // Optimized for List + + override def filter(p: A => Boolean): Self = filterImpl(p, isFlipped = false) + + override def filterNot(p: A => Boolean): Self = filterImpl(p, isFlipped = true) + + private[this] def filterImpl(p: A => Boolean, isFlipped: Boolean): Self = { + + // everything seen so far so far is not included + @tailrec def noneIn(l: Repr): Repr = { + if (l.isEmpty) + Nil.asInstanceOf[Repr] + else { + val h = l.head + val t = l.tail + if (p(h) != isFlipped) + allIn(l, t) + else + noneIn(t) + } + } + + // everything from 'start' is included, if everything from this point is in we can return the origin + // start otherwise if we discover an element that is out we must create a new partial list. + @tailrec def allIn(start: Repr, remaining: Repr): Repr = { + if (remaining.isEmpty) + start + else { + val x = remaining.head + if (p(x) != isFlipped) + allIn(start, remaining.tail) + else + partialFill(start, remaining) + } + } + + // we have seen elements that should be included then one that should be excluded, start building + def partialFill(origStart: Repr, firstMiss: Repr): Repr = { + val newHead = new ::(origStart.head, Nil) + var toProcess = origStart.tail + var currentLast = newHead + + // we know that all elements are :: until at least firstMiss.tail + while (!(toProcess eq firstMiss)) { + val newElem = new ::(toProcess.head, Nil) + currentLast.tl = newElem + currentLast = newElem + toProcess = toProcess.tail + } + + // at this point newHead points to a list which is a duplicate of all the 'in' elements up to the first miss. + // currentLast is the last element in that list. + + // now we are going to try and share as much of the tail as we can, only moving elements across when we have to. + var next = firstMiss.tail + var nextToCopy = next // the next element we would need to copy to our list if we cant share. + while (!next.isEmpty) { + // generally recommended is next.isNonEmpty but this incurs an extra method call. + val head: A = next.head + if (p(head) != isFlipped) { + next = next.tail + } else { + // its not a match - do we have outstanding elements? + while (!(nextToCopy eq next)) { + val newElem = new ::(nextToCopy.head, Nil) + currentLast.tl = newElem + currentLast = newElem + nextToCopy = nextToCopy.tail + } + nextToCopy = next.tail + next = next.tail + } + } + + // we have remaining elements - they are unchanged attach them to the end + if (!nextToCopy.isEmpty) + currentLast.tl = nextToCopy.asInstanceOf[List[A]] + + newHead.asInstanceOf[Repr] + } + + noneIn(repr) + } +}
\ No newline at end of file diff --git a/src/library/scala/collection/immutable/List.scala b/src/library/scala/collection/immutable/List.scala index 8e8bf953f3..e878f49c32 100644 --- a/src/library/scala/collection/immutable/List.scala +++ b/src/library/scala/collection/immutable/List.scala @@ -86,6 +86,7 @@ sealed abstract class List[+A] extends AbstractSeq[A] with Product with GenericTraversableTemplate[A, List] with LinearSeqOptimized[A, List[A]] + with FilteredTraversableInternal[A, List[A]] with Serializable { override def companion: GenericCompanion[List] = List @@ -416,6 +417,7 @@ sealed abstract class List[+A] extends AbstractSeq[A] // Create a proxy for Java serialization that allows us to avoid mutation // during de-serialization. This is the Serialization Proxy Pattern. protected final def writeReplace(): AnyRef = new List.SerializationProxy(this) + } /** The empty list. |