Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

++= in ArrayBuffer is optimized only for collection.mutable.IndexedSeq and not for all IndexedSeqs #4821

Closed
scabug opened this issue Jul 20, 2011 · 2 comments
Closed

++= in ArrayBuffer is optimized only for collection.mutable.IndexedSeq and not for all IndexedSeqs #4821

scabug opened this issue Jul 20, 2011 · 2 comments
Assignees
@paulp
Labels
enhancement

Comments

@scabug
Copy link

scabug commented Jul 20, 2011

The code for ++= in ArrayBuffer.scala is currently this:

  override def ++=(xs: TraversableOnce[A]): this.type = xs match {
    case v: IndexedSeq[_] =>
      val n = v.length
      ensureSize(size0 + n)
      v.copyToArray(array.asInstanceOf[scala.Array[Any]], size0, n)
      size0 += n
      this
    case _ =>
      super.++=(xs)
  }

However, the "case v: IndexedSeq[_]" only matches mutable IndexedSeq, whereas this optimization would also be valid for structures like the immutable Vector.
@scabug
Copy link
Author

scabug commented Jul 20, 2011

Imported From: https://issues.scala-lang.org/browse/SI-4821?orig=1
Reporter: Jean-Philippe Pellet (jpp)
Affected Versions: 2.8.1, 2.9.0

@scabug
Copy link
Author

scabug commented Aug 15, 2011

Commit Message Bot (anonymous) said:
(extempore in r25509) A conceivably pretty bad performance bug in builders.

#4821 pointed out that ArrayBuffer's ++ checks for a cheap size
method by matching on IndexedSeq, but mutable.IndexedSeq, so all
immutable collections are thrown in the same group as linear seqs.
I went looking for other examples of this and found them, in
key classes like Builder.

The "type shadowing trap" is a serious issue in the collections.
Closes #4821, no review.

@scabug scabug closed this as completed Aug 15, 2011
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees

@paulp paulp

Labels
enhancement
Projects
None yet
Milestone
No milestone
Development

No branches or pull requests
2 participants
@paulp @scabug