IndexedSeq.head uses isEmpty

Seq.isEmpty is lengthCompare and IndexedSeq
has efficient length aka knownSize. headOption
already uses isEmpty.

Author: som-snytt

library/src/scala/collection/IndexedSeq.scala

@@ -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 =
-    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)`