Conform foreach tparam to majority naming convention

'U' is the common choice for the foreach function result tparam.

This command summarises the naming diversity before and after this change.

$ fgrep -r 'def foreach[' *|cut -f2 -d:|cut -f1 -d'('|tr -s ' '|sed 's/override //g'|sort|uniq -c|sort -nr

Before,

     80  def foreach[U]
      6  def foreach[C]
      6  def foreach[B]
      4  final def foreach[U]
      3  def foreach[S]
      2  inline final def foreach[U]
      2  def foreach[A]
      1  inline final def foreach[specialized
      1  final def foreach[B]
      1  * def foreach[U]
      1  def foreach[Q]
      1  def foreach[D]
      1  def foreach[A,B,U]

After,

     98  def foreach[U]
      5  final def foreach[U]
      2  inline final def foreach[U]
      1  inline final def foreach[specialized
      1  * def foreach[U]
      1  def foreach[A,B,U]

(@ symbols removed.)

1 files changed, 3 insertions, 3 deletions

diff --git a/src/library/scala/collection/immutable/HashSet.scala b/src/library/scala/collection/immutable/HashSet.scala
index 27b2bfdde7..050e90b49b 100644
--- a/src/library/scala/collection/immutable/HashSet.scala
+++ b/src/library/scala/collection/immutable/HashSet.scala
@@ -53,7 +53,7 @@ class HashSet[A] extends AbstractSet[A]
 
   def iterator: Iterator[A] = Iterator.empty
 
-  override def foreach[U](f: A =>  U): Unit = { }
+  override def foreach[U](f: A => U): Unit = ()
 
   def contains(e: A): Boolean = get0(e, computeHash(e), 0)
 
@@ -215,7 +215,7 @@ object HashSet extends ImmutableSetFactory[HashSet] {
 
   private object EmptyHashSet extends HashSet[Any] { }
   private[collection] def emptyInstance: HashSet[Any] = EmptyHashSet
-  
+
   // utility method to create a HashTrieSet from two leaf HashSets (HashSet1 or HashSetCollision1) with non-colliding hash code)
   private def makeHashTrieSet[A](hash0:Int, elem0:HashSet[A], hash1:Int, elem1:HashSet[A], level:Int) : HashTrieSet[A] = {
     val index0 = (hash0 >>> level) & 0x1f
@@ -966,7 +966,7 @@ object HashSet extends ImmutableSetFactory[HashSet] {
       final override def getElem(cc: AnyRef): A = cc.asInstanceOf[HashSet1[A]].key
     }
 
-    override def foreach[U](f: A =>  U): Unit = {
+    override def foreach[U](f: A => U): Unit = {
       var i = 0
       while (i < elems.length) {
         elems(i).foreach(f)