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IndexedSeq#head now throws NoSuchElementException (not IndexOutOfBoundsException) #10392

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merged 2 commits into from
Jun 23, 2023
Merged

IndexedSeq#head now throws NoSuchElementException (not IndexOutOfBoundsException) #10392

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450363f
Translate outbound IndexOutOfBounds in IndexedSeq.head
som-snytt May 4, 2023
f3c5026
IndexedSeq.head uses isEmpty
som-snytt May 4, 2023
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IndexedSeq.head uses isEmpty 
Seq.isEmpty is lengthCompare and IndexedSeq
has efficient length aka knownSize. headOption
already uses isEmpty.
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@som-snytt
som-snytt committed May 4, 2023
commit f3c5026d3bbb68a25f0f21748970e72a554c7001
32 changes: 14 additions & 18 deletions src/library/scala/collection/IndexedSeq.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -92,28 +92,24 @@ trait IndexedSeqOps[+A, +CC[_], +C] extends Any with SeqOps[A, CC, C] { self =>
override def slice(from: Int, until: Int): C = fromSpecific(new IndexedSeqView.Slice(this, from, until))

override def head: A =
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wouldn't this now lead to repeated checks for isEmpty in {head,last}Option? should there be an @inline def headImpl: A = apply(0) and used in both head and headOption?

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My comment on the first commit is that head is fast. headOption is allocating.

try apply(0)
catch {
case e: IndexOutOfBoundsException =>
val what = self match {
case self: IndexedSeq[_] => self.collectionClassName
case _ => toString
}
throw new NoSuchElementException(s"head of empty $what")
}
if (!isEmpty) apply(0)
else throw new NoSuchElementException(s"head of empty ${
self match {
case self: IndexedSeq[_] => self.collectionClassName
case _ => toString
}
}")

override def headOption: Option[A] = if (isEmpty) None else Some(head)

override def last: A =
try apply(length - 1)
catch {
case e: IndexOutOfBoundsException =>
val what = self match {
case self: IndexedSeq[_] => self.collectionClassName
case _ => toString
}
throw new NoSuchElementException(s"last of empty $what")
}
if (!isEmpty) apply(length - 1)
else throw new NoSuchElementException(s"last of empty ${
self match {
case self: IndexedSeq[_] => self.collectionClassName
case _ => toString
}
}")

// We already inherit an efficient `lastOption = if (isEmpty) None else Some(last)`

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