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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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18 changes: 16 additions & 2 deletions src/library/scala/collection/IndexedSeq.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -91,11 +91,25 @@ 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 = apply(0)
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.

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 = apply(length - 1)
override def last: A =
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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7 changes: 7 additions & 0 deletions test/junit/scala/collection/mutable/ArrayDequeTest.scala
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Expand Up @@ -6,6 +6,7 @@ import org.junit.Assert._

import scala.annotation.nowarn
import scala.collection.SeqFactory
import scala.tools.testkit.AssertUtil.assertThrows

class ArrayDequeTest {

Expand Down Expand Up @@ -116,6 +117,12 @@ class ArrayDequeTest {
a.trimToSize() // Shrink to 256
assertEquals(a.capacity, 256)
}

@Test def `head of empty throws NoSuchElement`: Unit =
assertThrows[NoSuchElementException](ArrayDeque.empty[Int].head, _.endsWith("head of empty ArrayDeque"))

@Test def `last of empty throws NoSuchElement`: Unit =
assertThrows[NoSuchElementException](ArrayDeque.empty[Int].last, _.endsWith("last of empty ArrayDeque"))
}

object ArrayDequeTest {
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