Merge pull request scala/scala#9234 from NthPortal/topic/SeqView-Sorted-eager

Make SeqView.Sorted slightly less lazy

Author: lrytz

library/src/scala/collection/SeqView.scala

@@ -122,33 +122,40 @@ object SeqView {
  }
 
  @SerialVersionUID(3L)
- class Sorted[A, B >: A](private[this] var underlying: SomeSeqOps[A], ord: Ordering[B]) extends SeqView[A] {
+ class Sorted[A, B >: A] private (private[this] var underlying: SomeSeqOps[A],
+ private[this] val len: Int,
+ ord: Ordering[B])
+ extends SeqView[A] {
  outer =>
 
+ // force evaluation immediately by calling `length` so infinite collections
+ // hang on `sorted`/`sortWith`/`sortBy` rather than on arbitrary method calls
+ def this(underlying: SomeSeqOps[A], ord: Ordering[B]) = this(underlying, underlying.length, ord)
+
  @SerialVersionUID(3L)
  private[this] class ReverseSorted extends SeqView[A] {
  private[this] lazy val _reversed = new SeqView.Reverse(_sorted)
 
  def apply(i: Int): A = _reversed.apply(i)
- def length: Int = elems.length
+ def length: Int = len
  def iterator: Iterator[A] = Iterator.empty ++ _reversed.iterator // very lazy
- override def knownSize: Int = elems.knownSize
- override def isEmpty: Boolean = elems.isEmpty
+ override def knownSize: Int = len
+ override def isEmpty: Boolean = len == 0
  override def to[C1](factory: Factory[A, C1]): C1 = _reversed.to(factory)
  override def reverse: SeqView[A] = outer
  override protected def reversed: Iterable[A] = outer
 
  override def sorted[B1 >: A](implicit ord1: Ordering[B1]): SeqView[A] =
  if (ord1 == Sorted.this.ord) outer
  else if (ord1.isReverseOf(Sorted.this.ord)) this
- else new Sorted(elems, ord1)
+ else new Sorted(elems, len, ord1)
  }
 
  @volatile private[this] var evaluated = false
 
  private[this] lazy val _sorted: Seq[A] = {
  val res = {
- val len = underlying.length
+ val len = this.len
  if (len == 0) Nil
  else if (len == 1) List(underlying.head)
  else {
@@ -177,10 +184,10 @@ object SeqView {
  }
 
  def apply(i: Int): A = _sorted.apply(i)
- def length: Int = elems.length
+ def length: Int = len
  def iterator: Iterator[A] = Iterator.empty ++ _sorted.iterator // very lazy
- override def knownSize: Int = elems.knownSize
- override def isEmpty: Boolean = elems.isEmpty
+ override def knownSize: Int = len
+ override def isEmpty: Boolean = len == 0
  override def to[C1](factory: Factory[A, C1]): C1 = _sorted.to(factory)
  override def reverse: SeqView[A] = new ReverseSorted
  // we know `_sorted` is either tiny or has efficient random access,
@@ -190,7 +197,7 @@ object SeqView {
  override def sorted[B1 >: A](implicit ord1: Ordering[B1]): SeqView[A] =
  if (ord1 == this.ord) this
  else if (ord1.isReverseOf(this.ord)) reverse
- else new Sorted(elems, ord1)
+ else new Sorted(elems, len, ord1)
  }
 }