Imported From: https://issues.scala-lang.org/browse/SI-6628?orig=1
Reporter: @Atry
Affected Versions: 2.10.0-RC1
Other Milestones: 2.10.0

Sam Bock (nvt) said (edited on Nov 10, 2012 5:46:55 PM UTC):
It looks like this is a side effect of the change made in this commit on TraversableViewLike, which overrides isEmpty to forward to the underlying collection. It looks like forwarding has advantages in terms of performance, and avoids forcing the first element of the view. It is not correct when a view represents some subset of the original collection, however.

The simplest solution might be to override isEmpty for the transformed views that cannot simply forward to the underlying collections, which is (I believe) all of them except for Mapped. Barring a better suggestion, these could be overridden to return to their old, foreach based behavior.

@retronym said:
Promoting to blocker, it's a regression with reasonable workaround.

@retronym said:
Not sure which way to take this one. Ideas?

@paulp said:
I see no alternative to isEmpty walking the view until it finds an element or is exhausted, unless we're willing to do something like def isEmpty = underlying match { case x: View => x.slowIsEmpty ; case _ => underlying.isEmpty } .

@retronym said:
Sounds reasonable; will you submit a reversion?

@paulp said:
Yeah.

@paulp said:
scala/scala#1636