Applied suggestions to Vector cleanup

1 files changed, 161 insertions, 179 deletions

diff --git a/src/library/scala/collection/immutable/Vector.scala b/src/library/scala/collection/immutable/Vector.scala
index fa74e735ef..034691aea2 100644
--- a/src/library/scala/collection/immutable/Vector.scala
+++ b/src/library/scala/collection/immutable/Vector.scala
@@ -180,31 +180,36 @@ extends AbstractSeq[A]
       Vector.empty
   }
 
-  override /*IterableLike*/ def head: A = {
+  override /*IterableLike*/
+  def head: A = {
     if (isEmpty) throw new UnsupportedOperationException("empty.head")
     apply(0)
   }
 
-  override /*TraversableLike*/ def tail: Vector[A] = {
+  override /*TraversableLike*/
+  def tail: Vector[A] = {
     if (isEmpty) throw new UnsupportedOperationException("empty.tail")
     drop(1)
   }
 
-  override /*TraversableLike*/ def last: A = {
+  override /*TraversableLike*/
+  def last: A = {
     if (isEmpty) throw new UnsupportedOperationException("empty.last")
-    apply(length-1)
+    apply(length - 1)
   }
 
-  override /*TraversableLike*/ def init: Vector[A] = {
+  override /*TraversableLike*/
+  def init: Vector[A] = {
     if (isEmpty) throw new UnsupportedOperationException("empty.init")
     dropRight(1)
   }
 
-  override /*IterableLike*/ def slice(from: Int, until: Int): Vector[A] =
+  override /*IterableLike*/
+  def slice(from: Int, until: Int): Vector[A] =
     take(until).drop(from)
 
-  override /*IterableLike*/ def splitAt(n: Int): (Vector[A], Vector[A]) = (take(n), drop(n))
-
+  override /*IterableLike*/
+  def splitAt(n: Int): (Vector[A], Vector[A]) = (take(n), drop(n))
 
   // concat (suboptimal but avoids worst performance gotchas)
   override def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Vector[A], B, That]): That = {
@@ -258,7 +263,7 @@ extends AbstractSeq[A]
     dirty = true
   }
 
-  private[immutable] def appendFront[B>:A](value: B): Vector[B] = {
+  private[immutable] def appendFront[B >: A](value: B): Vector[B] = {
     if (endIndex != startIndex) {
       val blockIndex = (startIndex - 1) & ~31
       val lo = (startIndex - 1) & 31
@@ -272,9 +277,9 @@ extends AbstractSeq[A]
         s
       } else {
 
-        val freeSpace = ((1 << (5 * depth)) - endIndex) // free space at the right given the current tree-structure depth
-        val shift = (freeSpace & ~((1 << (5 * (depth - 1))) - 1)) // number of elements by which we'll shift right (only move at top level)
-        val shiftBlocks = (freeSpace >>> (5 * (depth - 1))) // number of top-level blocks
+        val freeSpace   = (1 << (5 * depth)) - endIndex               // free space at the right given the current tree-structure depth
+        val shift       = freeSpace & ~((1 << (5 * (depth - 1))) - 1) // number of elements by which we'll shift right (only move at top level)
+        val shiftBlocks = freeSpace >>> (5 * (depth - 1))             // number of top-level blocks
 
         if (shift != 0) {
           // case A: we can shift right on the top level
@@ -298,7 +303,7 @@ extends AbstractSeq[A]
             s.dirty = dirty
             s.shiftTopLevel(0, shiftBlocks) // shift right by n elements
             s.gotoPosWritable(newFocus, newBlockIndex, newFocus ^ newBlockIndex) // prepare for writing
-            s.display0(shift-1) = value.asInstanceOf[AnyRef]
+            s.display0(shift - 1) = value.asInstanceOf[AnyRef]
             s
           }
         } else if (blockIndex < 0) {
@@ -329,14 +334,14 @@ extends AbstractSeq[A]
       // empty vector, just insert single element at the back
       val elems = new Array[AnyRef](32)
       elems(31) = value.asInstanceOf[AnyRef]
-      val s = new Vector(31,32,0)
+      val s = new Vector(31, 32, 0)
       s.depth = 1
       s.display0 = elems
       s
     }
   }
 
-  private[immutable] def appendBack[B>:A](value: B): Vector[B] = {
+  private[immutable] def appendBack[B >: A](value: B): Vector[B] = {
     if (endIndex != startIndex) {
       val blockIndex = endIndex & ~31
       val lo = endIndex & 31
@@ -349,8 +354,8 @@ extends AbstractSeq[A]
         s.display0(lo) = value.asInstanceOf[AnyRef]
         s
       } else {
-        val shift = startIndex & ~((1 << 5 * (depth - 1)) - 1)
-        val shiftBlocks = startIndex >>> 5 * (depth - 1)
+        val shift       = startIndex & ~((1 << (5 * (depth - 1))) - 1)
+        val shiftBlocks = startIndex >>> (5 * (depth - 1))
 
         if (shift != 0) {
           if (depth > 1) {
@@ -389,7 +394,7 @@ extends AbstractSeq[A]
     } else {
       val elems = new Array[AnyRef](32)
       elems(0) = value.asInstanceOf[AnyRef]
-      val s = new Vector(0,1,0)
+      val s = new Vector(0, 1, 0)
       s.depth = 1
       s.display0 = elems
       s
@@ -415,22 +420,30 @@ extends AbstractSeq[A]
   }
 
   private def zeroLeft(array: Array[AnyRef], index: Int): Unit = {
-    var i = 0; while (i < index) { array(i) = null; i+=1 }
+    var i = 0
+    while (i < index) {
+      array(i) = null
+      i += 1
+    }
   }
 
   private def zeroRight(array: Array[AnyRef], index: Int): Unit = {
-    var i = index; while (i < array.length) { array(i) = null; i+=1 }
+    var i = index
+    while (i < array.length) {
+      array(i) = null
+      i += 1
+    }
   }
 
   private def copyLeft(array: Array[AnyRef], right: Int): Array[AnyRef] = {
-    val a2 = new Array[AnyRef](array.length)
-    java.lang.System.arraycopy(array, 0, a2, 0, right)
-    a2
+    val copy = new Array[AnyRef](array.length)
+    java.lang.System.arraycopy(array, 0, copy, 0, right)
+    copy
   }
   private def copyRight(array: Array[AnyRef], left: Int): Array[AnyRef] = {
-    val a2 = new Array[AnyRef](array.length)
-    java.lang.System.arraycopy(array, left, a2, left, a2.length - left)
-    a2
+    val copy = new Array[AnyRef](array.length)
+    java.lang.System.arraycopy(array, left, copy, left, copy.length - left)
+    copy
   }
 
   private def preClean(depth: Int) = {
@@ -462,38 +475,33 @@ extends AbstractSeq[A]
 
   // requires structure is at index cutIndex and writable at level 0
   private def cleanLeftEdge(cutIndex: Int) = {
-    if (cutIndex < (1 << 5)) {
+    if        (cutIndex < (1 <<  5)) {
       zeroLeft(display0, cutIndex)
-    } else
-    if (cutIndex < (1 << 10)) {
+    } else if (cutIndex < (1 << 10)) {
       zeroLeft(display0, cutIndex & 31)
-      display1 = copyRight(display1, (cutIndex >>>  5))
-    } else
-    if (cutIndex < (1 << 15)) {
+      display1 = copyRight(display1,  cutIndex >>>  5)
+    } else if (cutIndex < (1 << 15)) {
       zeroLeft(display0, cutIndex & 31)
       display1 = copyRight(display1, (cutIndex >>>  5) & 31)
-      display2 = copyRight(display2, (cutIndex >>> 10))
-    } else
-    if (cutIndex < (1 << 20)) {
+      display2 = copyRight(display2,  cutIndex >>> 10)
+    } else if (cutIndex < (1 << 20)) {
       zeroLeft(display0, cutIndex & 31)
       display1 = copyRight(display1, (cutIndex >>>  5) & 31)
       display2 = copyRight(display2, (cutIndex >>> 10) & 31)
-      display3 = copyRight(display3, (cutIndex >>> 15))
-    } else
-    if (cutIndex < (1 << 25)) {
+      display3 = copyRight(display3,  cutIndex >>> 15)
+    } else if (cutIndex < (1 << 25)) {
       zeroLeft(display0, cutIndex & 31)
       display1 = copyRight(display1, (cutIndex >>>  5) & 31)
       display2 = copyRight(display2, (cutIndex >>> 10) & 31)
       display3 = copyRight(display3, (cutIndex >>> 15) & 31)
-      display4 = copyRight(display4, (cutIndex >>> 20))
-    } else
-    if (cutIndex < (1 << 30)) {
+      display4 = copyRight(display4,  cutIndex >>> 20)
+    } else if (cutIndex < (1 << 30)) {
       zeroLeft(display0, cutIndex & 31)
       display1 = copyRight(display1, (cutIndex >>>  5) & 31)
       display2 = copyRight(display2, (cutIndex >>> 10) & 31)
       display3 = copyRight(display3, (cutIndex >>> 15) & 31)
       display4 = copyRight(display4, (cutIndex >>> 20) & 31)
-      display5 = copyRight(display5, (cutIndex >>> 25))
+      display5 = copyRight(display5,  cutIndex >>> 25)
     } else {
       throw new IllegalArgumentException()
     }
@@ -501,42 +509,36 @@ extends AbstractSeq[A]
 
   // requires structure is writable and at index cutIndex
   private def cleanRightEdge(cutIndex: Int) = {
-
     // we're actually sitting one block left if cutIndex lies on a block boundary
     // this means that we'll end up erasing the whole block!!
 
-    if (cutIndex <= (1 << 5)) {
+    if        (cutIndex <= (1 <<  5)) {
       zeroRight(display0, cutIndex)
-    } else
-    if (cutIndex <= (1 << 10)) {
-      zeroRight(display0, ((cutIndex-1) & 31) + 1)
-      display1 = copyLeft(display1, (cutIndex >>>  5))
-    } else
-    if (cutIndex <= (1 << 15)) {
-      zeroRight(display0, ((cutIndex-1) & 31) + 1)
-      display1 = copyLeft(display1, (((cutIndex-1) >>>  5) & 31) + 1)
-      display2 = copyLeft(display2, (cutIndex >>> 10))
-    } else
-    if (cutIndex <= (1 << 20)) {
-      zeroRight(display0, ((cutIndex-1) & 31) + 1)
-      display1 = copyLeft(display1, (((cutIndex-1) >>>  5) & 31) + 1)
-      display2 = copyLeft(display2, (((cutIndex-1) >>> 10) & 31) + 1)
-      display3 = copyLeft(display3, (cutIndex >>> 15))
-    } else
-    if (cutIndex <= (1 << 25)) {
-      zeroRight(display0, ((cutIndex-1) & 31) + 1)
-      display1 = copyLeft(display1, (((cutIndex-1) >>>  5) & 31) + 1)
-      display2 = copyLeft(display2, (((cutIndex-1) >>> 10) & 31) + 1)
-      display3 = copyLeft(display3, (((cutIndex-1) >>> 15) & 31) + 1)
-      display4 = copyLeft(display4, (cutIndex >>> 20))
-    } else
-    if (cutIndex <= (1 << 30)) {
-      zeroRight(display0, ((cutIndex-1) & 31) + 1)
-      display1 = copyLeft(display1, (((cutIndex-1) >>>  5) & 31) + 1)
-      display2 = copyLeft(display2, (((cutIndex-1) >>> 10) & 31) + 1)
-      display3 = copyLeft(display3, (((cutIndex-1) >>> 15) & 31) + 1)
-      display4 = copyLeft(display4, (((cutIndex-1) >>> 20) & 31) + 1)
-      display5 = copyLeft(display5, (cutIndex >>> 25))
+    } else if (cutIndex <= (1 << 10)) {
+      zeroRight(display0, ((cutIndex - 1) & 31) + 1)
+      display1 = copyLeft(display1, cutIndex >>>  5)
+    } else if (cutIndex <= (1 << 15)) {
+      zeroRight(display0, ((cutIndex - 1) & 31) + 1)
+      display1 = copyLeft(display1, (((cutIndex - 1) >>>  5) & 31) + 1)
+      display2 = copyLeft(display2, cutIndex >>> 10)
+    } else if (cutIndex <= (1 << 20)) {
+      zeroRight(display0, ((cutIndex - 1) & 31) + 1)
+      display1 = copyLeft(display1, (((cutIndex - 1) >>>  5) & 31) + 1)
+      display2 = copyLeft(display2, (((cutIndex - 1) >>> 10) & 31) + 1)
+      display3 = copyLeft(display3, cutIndex >>> 15)
+    } else if (cutIndex <= (1 << 25)) {
+      zeroRight(display0, ((cutIndex - 1) & 31) + 1)
+      display1 = copyLeft(display1, (((cutIndex - 1) >>>  5) & 31) + 1)
+      display2 = copyLeft(display2, (((cutIndex - 1) >>> 10) & 31) + 1)
+      display3 = copyLeft(display3, (((cutIndex - 1) >>> 15) & 31) + 1)
+      display4 = copyLeft(display4, cutIndex >>> 20)
+    } else if (cutIndex <= (1 << 30)) {
+      zeroRight(display0, ((cutIndex - 1) & 31) + 1)
+      display1 = copyLeft(display1, (((cutIndex - 1) >>>  5) & 31) + 1)
+      display2 = copyLeft(display2, (((cutIndex - 1) >>> 10) & 31) + 1)
+      display3 = copyLeft(display3, (((cutIndex - 1) >>> 15) & 31) + 1)
+      display4 = copyLeft(display4, (((cutIndex - 1) >>> 20) & 31) + 1)
+      display5 = copyLeft(display5, cutIndex >>> 25)
     } else {
       throw new IllegalArgumentException()
     }
@@ -556,11 +558,11 @@ extends AbstractSeq[A]
     val blockIndex = cutIndex & ~31
     val xor = cutIndex ^ (endIndex - 1)
     val d = requiredDepth(xor)
-    val shift = (cutIndex & ~((1 << (5 * d)) - 1))
+    val shift = cutIndex & ~((1 << (5 * d)) - 1)
 
     // need to init with full display iff going to cutIndex requires swapping block at level >= d
 
-    val s = new Vector(cutIndex-shift, endIndex-shift, blockIndex-shift)
+    val s = new Vector(cutIndex - shift, endIndex - shift, blockIndex - shift)
     s.initFrom(this)
     s.dirty = dirty
     s.gotoPosWritable(focus, blockIndex, focus ^ blockIndex)
@@ -573,14 +575,14 @@ extends AbstractSeq[A]
     val blockIndex = (cutIndex - 1) & ~31
     val xor = startIndex ^ (cutIndex - 1)
     val d = requiredDepth(xor)
-    val shift = (startIndex & ~((1 << (5 * d)) - 1))
+    val shift = startIndex & ~((1 << (5 * d)) - 1)
 
-    val s = new Vector(startIndex-shift, cutIndex-shift, blockIndex-shift)
+    val s = new Vector(startIndex - shift, cutIndex - shift, blockIndex - shift)
     s.initFrom(this)
     s.dirty = dirty
     s.gotoPosWritable(focus, blockIndex, focus ^ blockIndex)
     s.preClean(d)
-    s.cleanRightEdge(cutIndex-shift)
+    s.cleanRightEdge(cutIndex - shift)
     s
   }
 }
@@ -607,7 +609,7 @@ class VectorIterator[+A](_startIndex: Int, endIndex: Int)
 
     if (lo == endLo) {
       if (blockIndex + lo < endIndex) {
-        val newBlockIndex = blockIndex+32
+        val newBlockIndex = blockIndex + 32
         gotoNextBlockStart(newBlockIndex, blockIndex ^ newBlockIndex)
 
         blockIndex = newBlockIndex
@@ -634,7 +636,7 @@ class VectorIterator[+A](_startIndex: Int, endIndex: Int)
 }
 
 /** A class to build instances of `Vector`.  This builder is reusable. */
-final class VectorBuilder[A]() extends ReusableBuilder[A,Vector[A]] with VectorPointer[A @uncheckedVariance] {
+final class VectorBuilder[A]() extends ReusableBuilder[A, Vector[A]] with VectorPointer[A @uncheckedVariance] {
 
   // possible alternative: start with display0 = null, blockIndex = -32, lo = 32
   // to avoid allocating initial array if the result will be empty anyways
@@ -645,9 +647,9 @@ final class VectorBuilder[A]() extends ReusableBuilder[A,Vector[A]] with VectorP
   private var blockIndex = 0
   private var lo = 0
 
-  def += (elem: A): this.type = {
+  def +=(elem: A): this.type = {
     if (lo >= display0.length) {
-      val newBlockIndex = blockIndex+32
+      val newBlockIndex = blockIndex + 32
       gotoNextBlockStartWritable(newBlockIndex, blockIndex ^ newBlockIndex)
       blockIndex = newBlockIndex
       lo = 0
@@ -657,8 +659,7 @@ final class VectorBuilder[A]() extends ReusableBuilder[A,Vector[A]] with VectorP
     this
   }
 
-  override def ++=(xs: TraversableOnce[A]): this.type =
-    super.++=(xs)
+  override def ++=(xs: TraversableOnce[A]): this.type = super.++=(xs)
 
   def result: Vector[A] = {
     val size = blockIndex + lo
@@ -678,9 +679,8 @@ final class VectorBuilder[A]() extends ReusableBuilder[A,Vector[A]] with VectorP
   }
 }
 
-
 private[immutable] trait VectorPointer[T] {
-    private[immutable] var depth: Int = _
+    private[immutable] var depth:    Int = _
     private[immutable] var display0: Array[AnyRef] = _
     private[immutable] var display1: Array[AnyRef] = _
     private[immutable] var display2: Array[AnyRef] = _
@@ -725,63 +725,52 @@ private[immutable] trait VectorPointer[T] {
       }
     }
 
-
     // requires structure is at pos oldIndex = xor ^ index
     private[immutable] final def getElem(index: Int, xor: Int): T = {
-      if (xor < (1 << 5)) { // level = 0
+      if        (xor < (1 <<  5)) { // level = 0
         display0(index & 31).asInstanceOf[T]
-      } else
-      if (xor < (1 << 10)) { // level = 1
-        display1((index >> 5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
-      } else
-      if (xor < (1 << 15)) { // level = 2
-        display2((index >> 10) & 31).asInstanceOf[Array[AnyRef]]((index >> 5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
-      } else
-      if (xor < (1 << 20)) { // level = 3
-        display3((index >> 15) & 31).asInstanceOf[Array[AnyRef]]((index >> 10) & 31).asInstanceOf[Array[AnyRef]]((index >> 5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
-      } else
-      if (xor < (1 << 25)) { // level = 4
-        display4((index >> 20) & 31).asInstanceOf[Array[AnyRef]]((index >> 15) & 31).asInstanceOf[Array[AnyRef]]((index >> 10) & 31).asInstanceOf[Array[AnyRef]]((index >> 5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
-      } else
-      if (xor < (1 << 30)) { // level = 5
+      } else if (xor < (1 << 10)) { // level = 1
+        display1((index >>  5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
+      } else if (xor < (1 << 15)) { // level = 2
+        display2((index >> 10) & 31).asInstanceOf[Array[AnyRef]]((index >>  5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
+      } else if (xor < (1 << 20)) { // level = 3
+        display3((index >> 15) & 31).asInstanceOf[Array[AnyRef]]((index >> 10) & 31).asInstanceOf[Array[AnyRef]]((index >>  5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
+      } else if (xor < (1 << 25)) { // level = 4
+        display4((index >> 20) & 31).asInstanceOf[Array[AnyRef]]((index >> 15) & 31).asInstanceOf[Array[AnyRef]]((index >> 10) & 31).asInstanceOf[Array[AnyRef]]((index >>  5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
+      } else if (xor < (1 << 30)) { // level = 5
         display5((index >> 25) & 31).asInstanceOf[Array[AnyRef]]((index >> 20) & 31).asInstanceOf[Array[AnyRef]]((index >> 15) & 31).asInstanceOf[Array[AnyRef]]((index >> 10) & 31).asInstanceOf[Array[AnyRef]]((index >> 5) & 31).asInstanceOf[Array[AnyRef]](index & 31).asInstanceOf[T]
-      } else { // level = 6
+      } else {                      // level = 6
         throw new IllegalArgumentException()
       }
     }
 
-
     // go to specific position
     // requires structure is at pos oldIndex = xor ^ index,
     // ensures structure is at pos index
     private[immutable] final def gotoPos(index: Int, xor: Int): Unit = {
-      if (xor < (1 << 5)) { // level = 0 (could maybe removed)
-      } else
-      if (xor < (1 << 10)) { // level = 1
+      if        (xor < (1 <<  5)) { // level = 0
+        // we're already at the block start pos
+      } else if (xor < (1 << 10)) { // level = 1
         display0 = display1((index >>  5) & 31).asInstanceOf[Array[AnyRef]]
-      } else
-      if (xor < (1 << 15)) { // level = 2
+      } else if (xor < (1 << 15)) { // level = 2
         display1 = display2((index >> 10) & 31).asInstanceOf[Array[AnyRef]]
         display0 = display1((index >>  5) & 31).asInstanceOf[Array[AnyRef]]
-      } else
-      if (xor < (1 << 20)) { // level = 3
+      } else if (xor < (1 << 20)) { // level = 3
         display2 = display3((index >> 15) & 31).asInstanceOf[Array[AnyRef]]
         display1 = display2((index >> 10) & 31).asInstanceOf[Array[AnyRef]]
         display0 = display1((index >>  5) & 31).asInstanceOf[Array[AnyRef]]
-      } else
-      if (xor < (1 << 25)) { // level = 4
+      } else if (xor < (1 << 25)) { // level = 4
         display3 = display4((index >> 20) & 31).asInstanceOf[Array[AnyRef]]
         display2 = display3((index >> 15) & 31).asInstanceOf[Array[AnyRef]]
         display1 = display2((index >> 10) & 31).asInstanceOf[Array[AnyRef]]
         display0 = display1((index >>  5) & 31).asInstanceOf[Array[AnyRef]]
-      } else
-      if (xor < (1 << 30)) { // level = 5
+      } else if (xor < (1 << 30)) { // level = 5
         display4 = display5((index >> 25) & 31).asInstanceOf[Array[AnyRef]]
         display3 = display4((index >> 20) & 31).asInstanceOf[Array[AnyRef]]
         display2 = display3((index >> 15) & 31).asInstanceOf[Array[AnyRef]]
         display1 = display2((index >> 10) & 31).asInstanceOf[Array[AnyRef]]
         display0 = display1((index >>  5) & 31).asInstanceOf[Array[AnyRef]]
-      } else { // level = 6
+      } else {                      // level = 6
         throw new IllegalArgumentException()
       }
     }
@@ -790,31 +779,27 @@ private[immutable] trait VectorPointer[T] {
 
     // xor: oldIndex ^ index
     private[immutable] final def gotoNextBlockStart(index: Int, xor: Int): Unit = { // goto block start pos
-      if (xor < (1 << 10)) { // level = 1
+      if        (xor < (1 << 10)) { // level = 1
         display0 = display1((index >>  5) & 31).asInstanceOf[Array[AnyRef]]
-      } else
-      if (xor < (1 << 15)) { // level = 2
+      } else if (xor < (1 << 15)) { // level = 2
         display1 = display2((index >> 10) & 31).asInstanceOf[Array[AnyRef]]
         display0 = display1(0).asInstanceOf[Array[AnyRef]]
-      } else
-      if (xor < (1 << 20)) { // level = 3
+      } else if (xor < (1 << 20)) { // level = 3
         display2 = display3((index >> 15) & 31).asInstanceOf[Array[AnyRef]]
         display1 = display2(0).asInstanceOf[Array[AnyRef]]
         display0 = display1(0).asInstanceOf[Array[AnyRef]]
-      } else
-      if (xor < (1 << 25)) { // level = 4
+      } else if (xor < (1 << 25)) { // level = 4
         display3 = display4((index >> 20) & 31).asInstanceOf[Array[AnyRef]]
         display2 = display3(0).asInstanceOf[Array[AnyRef]]
         display1 = display2(0).asInstanceOf[Array[AnyRef]]
         display0 = display1(0).asInstanceOf[Array[AnyRef]]
-      } else
-      if (xor < (1 << 30)) { // level = 5
+      } else if (xor < (1 << 30)) { // level = 5
         display4 = display5((index >> 25) & 31).asInstanceOf[Array[AnyRef]]
         display3 = display4(0).asInstanceOf[Array[AnyRef]]
         display2 = display3(0).asInstanceOf[Array[AnyRef]]
         display1 = display2(0).asInstanceOf[Array[AnyRef]]
         display0 = display1(0).asInstanceOf[Array[AnyRef]]
-      } else { // level = 6
+      } else {                      // level = 6
         throw new IllegalArgumentException()
       }
     }
@@ -823,29 +808,34 @@ private[immutable] trait VectorPointer[T] {
 
     // xor: oldIndex ^ index
     private[immutable] final def gotoNextBlockStartWritable(index: Int, xor: Int): Unit = { // goto block start pos
-      if (xor < (1 << 10)) { // level = 1
-        if (depth == 1) { display1 = new Array(32); display1(0) = display0; depth+=1}
+      if        (xor < (1 << 10)) { // level = 1
+        if (depth == 1) {
+          display1 = new Array(32); display1(0) = display0; depth += 1
+        }
         display0 = new Array(32)
         display1((index >>  5) & 31) = display0
-      } else
-      if (xor < (1 << 15)) { // level = 2
-        if (depth == 2) { display2 = new Array(32); display2(0) = display1; depth+=1}
+      } else if (xor < (1 << 15)) { // level = 2
+        if (depth == 2) {
+          display2 = new Array(32); display2(0) = display1; depth += 1
+        }
         display0 = new Array(32)
         display1 = new Array(32)
         display1((index >>  5) & 31) = display0
         display2((index >> 10) & 31) = display1
-      } else
-      if (xor < (1 << 20)) { // level = 3
-        if (depth == 3) { display3 = new Array(32); display3(0) = display2; depth+=1}
+      } else if (xor < (1 << 20)) { // level = 3
+        if (depth == 3) {
+          display3 = new Array(32); display3(0) = display2; depth += 1
+        }
         display0 = new Array(32)
         display1 = new Array(32)
         display2 = new Array(32)
         display1((index >>  5) & 31) = display0
         display2((index >> 10) & 31) = display1
         display3((index >> 15) & 31) = display2
-      } else
-      if (xor < (1 << 25)) { // level = 4
-        if (depth == 4) { display4 = new Array(32); display4(0) = display3; depth+=1}
+      } else if (xor < (1 << 25)) { // level = 4
+        if (depth == 4) {
+          display4 = new Array(32); display4(0) = display3; depth += 1
+        }
         display0 = new Array(32)
         display1 = new Array(32)
         display2 = new Array(32)
@@ -854,9 +844,10 @@ private[immutable] trait VectorPointer[T] {
         display2((index >> 10) & 31) = display1
         display3((index >> 15) & 31) = display2
         display4((index >> 20) & 31) = display3
-      } else
-      if (xor < (1 << 30)) { // level = 5
-        if (depth == 5) { display5 = new Array(32); display5(0) = display4; depth+=1}
+      } else if (xor < (1 << 30)) { // level = 5
+        if (depth == 5) {
+          display5 = new Array(32); display5(0) = display4; depth += 1
+        }
         display0 = new Array(32)
         display1 = new Array(32)
         display2 = new Array(32)
@@ -867,20 +858,20 @@ private[immutable] trait VectorPointer[T] {
         display3((index >> 15) & 31) = display2
         display4((index >> 20) & 31) = display3
         display5((index >> 25) & 31) = display4
-      } else { // level = 6
+      } else {                      // level = 6
         throw new IllegalArgumentException()
       }
     }
 
     // STUFF BELOW USED BY APPEND / UPDATE
 
-    private[immutable] final def copyOf(a: Array[AnyRef]) = {
-      val b = new Array[AnyRef](a.length)
-      java.lang.System.arraycopy(a, 0, b, 0, a.length)
-      b
+    private[immutable] final def copyOf(a: Array[AnyRef]): Array[AnyRef] = {
+      val copy = new Array[AnyRef](a.length)
+      java.lang.System.arraycopy(a, 0, copy, 0, a.length)
+      copy
     }
 
-    private[immutable] final def nullSlotAndCopy(array: Array[AnyRef], index: Int) = {
+    private[immutable] final def nullSlotAndCopy(array: Array[AnyRef], index: Int): Array[AnyRef] = {
       val x = array(index)
       array(index) = null
       copyOf(x.asInstanceOf[Array[AnyRef]])
@@ -970,23 +961,20 @@ private[immutable] trait VectorPointer[T] {
     // requires structure is dirty and at pos oldIndex,
     // ensures structure is dirty and at pos newIndex and writable at level 0
     private[immutable] final def gotoPosWritable1(oldIndex: Int, newIndex: Int, xor: Int): Unit = {
-      if (xor < (1 <<  5)) { // level = 0
+      if        (xor < (1 <<  5)) { // level = 0
         display0 = copyOf(display0)
-      } else
-      if (xor < (1 << 10)) { // level = 1
+      } else if (xor < (1 << 10)) { // level = 1
         display1 = copyOf(display1)
-        display1((oldIndex >> 5) & 31) = display0
+        display1((oldIndex >>  5) & 31) = display0
         display0 = nullSlotAndCopy(display1, (newIndex >>  5) & 31)
-      } else
-      if (xor < (1 << 15)) { // level = 2
+      } else if (xor < (1 << 15)) { // level = 2
         display1 = copyOf(display1)
         display2 = copyOf(display2)
         display1((oldIndex >>  5) & 31) = display0
         display2((oldIndex >> 10) & 31) = display1
         display1 = nullSlotAndCopy(display2, (newIndex >> 10) & 31)
         display0 = nullSlotAndCopy(display1, (newIndex >>  5) & 31)
-      } else
-      if (xor < (1 << 20)) { // level = 3
+      } else if (xor < (1 << 20)) { // level = 3
         display1 = copyOf(display1)
         display2 = copyOf(display2)
         display3 = copyOf(display3)
@@ -996,8 +984,7 @@ private[immutable] trait VectorPointer[T] {
         display2 = nullSlotAndCopy(display3, (newIndex >> 15) & 31)
         display1 = nullSlotAndCopy(display2, (newIndex >> 10) & 31)
         display0 = nullSlotAndCopy(display1, (newIndex >>  5) & 31)
-      } else
-      if (xor < (1 << 25)) { // level = 4
+      } else if (xor < (1 << 25)) { // level = 4
         display1 = copyOf(display1)
         display2 = copyOf(display2)
         display3 = copyOf(display3)
@@ -1010,8 +997,7 @@ private[immutable] trait VectorPointer[T] {
         display2 = nullSlotAndCopy(display3, (newIndex >> 15) & 31)
         display1 = nullSlotAndCopy(display2, (newIndex >> 10) & 31)
         display0 = nullSlotAndCopy(display1, (newIndex >>  5) & 31)
-      } else
-      if (xor < (1 << 30)) { // level = 5
+      } else if (xor < (1 << 30)) { // level = 5
         display1 = copyOf(display1)
         display2 = copyOf(display2)
         display3 = copyOf(display3)
@@ -1027,7 +1013,7 @@ private[immutable] trait VectorPointer[T] {
         display2 = nullSlotAndCopy(display3, (newIndex >> 15) & 31)
         display1 = nullSlotAndCopy(display2, (newIndex >> 10) & 31)
         display0 = nullSlotAndCopy(display1, (newIndex >>  5) & 31)
-      } else { // level = 6
+      } else {                      // level = 6
         throw new IllegalArgumentException()
       }
     }
@@ -1037,7 +1023,7 @@ private[immutable] trait VectorPointer[T] {
 
     private[immutable] final def copyRange(array: Array[AnyRef], oldLeft: Int, newLeft: Int) = {
       val elems = new Array[AnyRef](32)
-      java.lang.System.arraycopy(array, oldLeft, elems, newLeft, 32 - math.max(newLeft,oldLeft))
+      java.lang.System.arraycopy(array, oldLeft, elems, newLeft, 32 - math.max(newLeft, oldLeft))
       elems
     }
 
@@ -1048,43 +1034,40 @@ private[immutable] trait VectorPointer[T] {
     // requires structure is clean and at pos oldIndex,
     // ensures structure is dirty and at pos newIndex and writable at level 0
     private[immutable] final def gotoFreshPosWritable0(oldIndex: Int, newIndex: Int, xor: Int): Unit = { // goto block start pos
-      if (xor < (1 << 5)) { // level = 0
-      } else
-      if (xor < (1 << 10)) { // level = 1
+      if        (xor < (1 <<  5)) { // level = 0
+        // we're already at the block start
+      } else if (xor < (1 << 10)) { // level = 1
         if (depth == 1) {
           display1 = new Array(32)
           display1((oldIndex >>  5) & 31) = display0
-          depth +=1
+          depth += 1
         }
         display0 = new Array(32)
-      } else
-      if (xor < (1 << 15)) { // level = 2
+      } else if (xor < (1 << 15)) { // level = 2
         if (depth == 2) {
           display2 = new Array(32)
           display2((oldIndex >> 10) & 31) = display1
-          depth +=1
+          depth += 1
         }
         display1 = display2((newIndex >> 10) & 31).asInstanceOf[Array[AnyRef]]
         if (display1 == null) display1 = new Array(32)
         display0 = new Array(32)
-      } else
-      if (xor < (1 << 20)) { // level = 3
+      } else if (xor < (1 << 20)) { // level = 3
         if (depth == 3) {
           display3 = new Array(32)
           display3((oldIndex >> 15) & 31) = display2
-          depth +=1
+          depth += 1
         }
         display2 = display3((newIndex >> 15) & 31).asInstanceOf[Array[AnyRef]]
         if (display2 == null) display2 = new Array(32)
         display1 = display2((newIndex >> 10) & 31).asInstanceOf[Array[AnyRef]]
         if (display1 == null) display1 = new Array(32)
         display0 = new Array(32)
-      } else
-      if (xor < (1 << 25)) { // level = 4
+      } else if (xor < (1 << 25)) { // level = 4
         if (depth == 4) {
           display4 = new Array(32)
           display4((oldIndex >> 20) & 31) = display3
-          depth +=1
+          depth += 1
         }
         display3 = display4((newIndex >> 20) & 31).asInstanceOf[Array[AnyRef]]
         if (display3 == null) display3 = new Array(32)
@@ -1093,12 +1076,11 @@ private[immutable] trait VectorPointer[T] {
         display1 = display2((newIndex >> 10) & 31).asInstanceOf[Array[AnyRef]]
         if (display1 == null) display1 = new Array(32)
         display0 = new Array(32)
-      } else
-      if (xor < (1 << 30)) { // level = 5
+      } else if (xor < (1 << 30)) { // level = 5
         if (depth == 5) {
           display5 = new Array(32)
-          display5((oldIndex >>  25) & 31) = display4
-          depth +=1
+          display5((oldIndex >> 25) & 31) = display4
+          depth += 1
         }
         display4 = display5((newIndex >> 25) & 31).asInstanceOf[Array[AnyRef]]
         if (display4 == null) display4 = new Array(32)
@@ -1109,7 +1091,7 @@ private[immutable] trait VectorPointer[T] {
         display1 = display2((newIndex >> 10) & 31).asInstanceOf[Array[AnyRef]]
         if (display1 == null) display1 = new Array(32)
         display0 = new Array(32)
-      } else { // level = 6
+      } else {                      // level = 6
         throw new IllegalArgumentException()
       }
     }