SI-9605 Searching does not use binary search for Array

Binary search should be used for every `IndexedSeqLike` instance and not only for `IndexedSeq`. According the Scaladoc, it is `IndexedSeqLike` that guarantees "constant-time or near constant-time element access and length computation".

1 files changed, 48 insertions, 0 deletions

diff --git a/test/junit/scala/collection/SearchingTest.scala b/test/junit/scala/collection/SearchingTest.scala
new file mode 100644
index 0000000000..2f939d625e
--- /dev/null
+++ b/test/junit/scala/collection/SearchingTest.scala
@@ -0,0 +1,48 @@
+package scala.collection
+
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.junit.Assert._
+import org.junit.Test
+import scala.collection.Searching._
+
+@RunWith(classOf[JUnit4])
+class SearchingTest {
+
+  @Test
+  def doesLinearSearchOnLinearSeqs() {
+
+    class TestSeq[A](list: List[A]) extends SeqLike[A, TestSeq[A]] {
+      var elementsAccessed = Set.empty[Int]
+
+      protected[this] def newBuilder = ??? // not needed for this test
+      def seq = list
+      def iterator = list.iterator
+      def length = list.length
+      def apply(idx: Int) = { elementsAccessed += idx; list(idx) }
+    }
+
+    val coll = new TestSeq((0 to 6).toList)
+
+    assertEquals(Found(5), coll.search(5))
+    assertEquals(Set.empty, coll.elementsAccessed) // linear search should not access elements via apply()
+  }
+
+  @Test
+  def doesBinarySearchOnIndexedSeqs() {
+
+    class TestIndexedSeq[A](vec: Vector[A]) extends IndexedSeqLike[A, TestIndexedSeq[A]] {
+      var elementsAccessed = Set.empty[Int]
+
+      protected[this] def newBuilder = ??? // not needed for this test
+      def seq = vec
+      def length = vec.length
+      def apply(idx: Int) = { elementsAccessed += idx; vec(idx) }
+    }
+
+    val coll = new TestIndexedSeq((0 to 6).toVector)
+
+    assertEquals(Found(5), coll.search(5))
+    assertEquals(Set(3, 5), coll.elementsAccessed)
+  }
+}