Deleted method rotateAt and added applyO

src/main/scala/scala/collection/decorators/SeqDecorator.scala

@@ -69,6 +69,18 @@ class SeqDecorator[C, S <: IsSeq[C]](coll: C)(implicit val seq: S) {
   private def index(i: IndexO): Index =
     java.lang.Math.floorMod(i, seq(coll).size)
 
+  /** Gets the element at some circular index.
+   *
+   * @param i circular index
+   * @return the element of the sequence at the given index
+   * @throws java.lang.ArithmeticException if the sequence is empty
+   * @example {{{
+   *      Seq(0, 1, 2).applyO(3) => 0
+   * }}}
+   */
+  def applyO(i: IndexO): this.seq.A =
+    seq(coll).apply(index(i))
+
   /** Considers the sequence circular and rotates it right by `step` places.
    *
    * @param step the number of places to be rotated to the right
@@ -100,17 +112,4 @@ class SeqDecorator[C, S <: IsSeq[C]](coll: C)(implicit val seq: S) {
   def rotateLeft[B >: seq.A, That](step: Int)(implicit bf: BuildFrom[C, B, That]): That =
     rotateRight(-step)
 
-  /** Considers the sequence circular and rotates it to start with the element at `i` circular index.
-   *
-   * @param i the circular index of the element to be rotated at the start of the new collection
-   * @tparam B the element type of the returned collection
-   * @return a new collection consisting of all elements of this collection
-   *         circularly rotated so to start with the element at circular index `i`.
-   * @example {{{
-   *      List(1, 2, 3, 4, 5).startAt(2) => List(3, 4, 5, 1, 2)
-   * }}}
-   */
-  def startAt[B >: seq.A, That](i: IndexO)(implicit bf: BuildFrom[C, B, That]): That =
-    rotateLeft(i)
-
 }

src/test/scala/scala/collection/decorators/SeqDecoratorTest.scala

@@ -1,7 +1,7 @@
 package scala.collection
 package decorators
 
-import org.junit.Assert.assertEquals
+import org.junit.Assert.{assertEquals, assertSame, assertThrows}
 import org.junit.Test
 import scala.collection.immutable._
 
@@ -46,6 +46,13 @@ class SeqDecoratorTest {
     assertEquals(s.replaced(4, 4), s)
   }
 
+  @Test def testApplyO(): Unit = {
+    val s = Seq(0, 1, 2)
+    assertEquals(s.applyO(3), 0)
+    val empty = Vector.empty[Int]
+    assertThrows(classOf[java.lang.ArithmeticException], () => empty.applyO(1))
+  }
+
   @Test def testRotatedRight(): Unit = {
     val s = Seq(1, 2, 3, 2, 1)
     val sRotated = Seq(1, 1, 2, 3, 2)
@@ -66,12 +73,4 @@ class SeqDecoratorTest {
     assertEquals(s.rotateLeft(-4), sRotated)
   }
 
-  @Test def testStartedAt(): Unit = {
-    val s = Seq(1, 2, 3, 2, 1)
-    val sRotated = Seq(2, 3, 2, 1, 1)
-    assertEquals(s.startAt(1), sRotated)
-    assertEquals(s.startAt(6), sRotated)
-    assertEquals(s.startAt(-4), sRotated)
-  }
-
 }