Closes #2540 and closes #2593.

2 files changed, 46 insertions, 24 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 58146ffd80..59362e2874 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -3898,26 +3898,7 @@ trait Typers { self: Analyzer =>
           if (util.Statistics.enabled) selcnt += 1
           var qual1 = checkDead(typedQualifier(qual, mode))
           if (name.isTypeName) qual1 = checkStable(qual1)
-
-          val tree1 = // temporarily use `filter' and an alternative for `withFilter'
-            if (name == nme.withFilter)
-              silent(_ => typedSelect(qual1, name)) match {
-                case result1: Tree =>
-                  result1
-                case ex1: TypeError =>
-                  silent(_ => typed1(Select(qual1, nme.filter) setPos tree.pos, mode, pt)) match {
-                    case result2: Tree =>
-                      unit.deprecationWarning(
-                        tree.pos, "`withFilter' method does not yet exist on "+qual1.tpe.widen+
-                        ", using `filter' method instead")
-                      result2
-                    case ex2: TypeError =>
-                      reportTypeError(tree.pos, ex1)
-                      setError(tree)
-                  }
-              }
-            else
-              typedSelect(qual1, name)
+          val tree1 = typedSelect(qual1, name)
 
           if (qual1.symbol == RootPackage) treeCopy.Ident(tree1, name)
           else tree1
diff --git a/src/library/scala/collection/Iterator.scala b/src/library/scala/collection/Iterator.scala
index 8f49bbd0e4..b507426fb8 100644
--- a/src/library/scala/collection/Iterator.scala
+++ b/src/library/scala/collection/Iterator.scala
@@ -367,11 +367,52 @@ trait Iterator[+A] { self =>
     def next() = if (hasNext) { hdDefined = false; hd } else empty.next()
   }
 
+  def withFilter(p: A => Boolean): WithFilter = new WithFilter(p)
 
-  /** !!! Temporary, awaiting more general implementation.
-   *  ... better wait longer, this fails once flatMap gets in the mix.
-   */
-  // def withFilter(p: A => Boolean) = this.toStream withFilter p
+  final class WithFilter private[Iterator] (p: A => Boolean) {
+
+    def map[B](f: A => B): Iterator[B] = new Iterator[B] {
+      private var hd: A = _
+      private var hdDefined: Boolean = false
+
+      def hasNext: Boolean = hdDefined || {
+        do {
+          if (!self.hasNext) return false
+          hd = self.next()
+        } while (!p(hd))
+        hdDefined = true
+        true
+      }
+
+      def next() = if (hasNext) { hdDefined = false; f(hd) } else empty.next()
+    }
+
+    def flatMap[B](f: A => Iterator[B]): Iterator[B] = new Iterator[B] {
+      private var cur: Iterator[B] = empty
+
+      @tailrec
+      def hasNext: Boolean = cur.hasNext || {
+        var x = null.asInstanceOf[A]
+        do {
+          if (!self.hasNext) return false
+          x = self.next()
+        } while (!p(x))
+        cur = f(x)
+        hasNext
+      }
+
+      def next(): B = (if (hasNext) cur else empty).next()
+    }
+
+    def foreach[U](f: A => U) {
+      while (self.hasNext) {
+        val x = self.next()
+        if (p(x)) f(x)
+      }
+    }
+
+    def withFilter(q: A => Boolean): WithFilter = new WithFilter(x => p(x) && q(x))
+  }
 
   /** Returns an iterator over all the elements of this iterator which
    *  do not satisfy the predicate <code>p</code>.