Gave StringBuilder a StringLike parent as endor...

Gave StringBuilder a StringLike parent as endorsed by martin in
http://www.scala-lang.org/node/6893 . Review by odersky.

6 files changed, 29 insertions, 10 deletions

diff --git a/src/library/scala/Predef.scala b/src/library/scala/Predef.scala
index 3c44a1f992..820d1bb20f 100644
--- a/src/library/scala/Predef.scala
+++ b/src/library/scala/Predef.scala
@@ -289,8 +289,8 @@ object Predef extends LowPriorityImplicits {
 
   implicit def stringCanBuildFrom: CanBuildFrom[String, Char, String] =
     new CanBuildFrom[String, Char, String] {
-      def apply(from: String) = new scala.collection.mutable.StringBuilder
-      def apply() = new scala.collection.mutable.StringBuilder
+      def apply(from: String) = apply()
+      def apply() = scala.collection.mutable.StringBuilder.newBuilder
     }
 
   implicit def seqToCharSequence(xs: collection.IndexedSeq[Char]): CharSequence = new CharSequence {
diff --git a/src/library/scala/collection/immutable/StringLike.scala b/src/library/scala/collection/immutable/StringLike.scala
index 6fe6b4555d..9c137810ac 100644
--- a/src/library/scala/collection/immutable/StringLike.scala
+++ b/src/library/scala/collection/immutable/StringLike.scala
@@ -42,7 +42,7 @@ import StringLike._
  *  @define mayNotTerminateInf
  *  @define willNotTerminateInf
  */
-trait StringLike[+Repr] extends IndexedSeqOptimized[Char, Repr] with Ordered[String] {
+trait StringLike[+Repr] extends collection.IndexedSeqOptimized[Char, Repr] with Ordered[String] {
 self =>
 
   /** Creates a string builder buffer as builder for this class */
diff --git a/src/library/scala/collection/immutable/StringOps.scala b/src/library/scala/collection/immutable/StringOps.scala
index 0d8f5f6b83..a18a30db01 100644
--- a/src/library/scala/collection/immutable/StringOps.scala
+++ b/src/library/scala/collection/immutable/StringOps.scala
@@ -34,7 +34,7 @@ final class StringOps(override val repr: String) extends StringLike[String] {
   override protected[this] def toCollection(repr: String): WrappedString = new WrappedString(repr)
 
   /** Creates a string builder buffer as builder for this class */
-  override protected[this] def newBuilder = new StringBuilder
+  override protected[this] def newBuilder = StringBuilder.newBuilder
 
   override def slice(from: Int, until: Int): String = {
     /** Slice must be forgiving on all out of bounds indices and
diff --git a/src/library/scala/collection/immutable/WrappedString.scala b/src/library/scala/collection/immutable/WrappedString.scala
index 8fe3a2bc5c..62a39213d5 100644
--- a/src/library/scala/collection/immutable/WrappedString.scala
+++ b/src/library/scala/collection/immutable/WrappedString.scala
@@ -46,5 +46,5 @@ class WrappedString(override val self: String) extends IndexedSeq[Char] with Str
  *  @since 2.8
  */
 object WrappedString {
-  def newBuilder: Builder[Char, WrappedString] = new StringBuilder() mapResult (new WrappedString(_))
+  def newBuilder: Builder[Char, WrappedString] = StringBuilder.newBuilder mapResult (x => new WrappedString(x))
 }
diff --git a/src/library/scala/collection/mutable/StringBuilder.scala b/src/library/scala/collection/mutable/StringBuilder.scala
index e9258c9730..f78131111a 100644
--- a/src/library/scala/collection/mutable/StringBuilder.scala
+++ b/src/library/scala/collection/mutable/StringBuilder.scala
@@ -11,6 +11,7 @@ package mutable
 
 import java.lang.{ StringBuilder => JavaStringBuilder }
 import annotation.migration
+import immutable.StringLike
 
 /** A builder for mutable sequence of characters.  This class provides an API
  *  mostly compatible with java.lang.StringBuilder, except where there are conflicts
@@ -24,10 +25,16 @@ import annotation.migration
 @serializable
 @SerialVersionUID(0 - 8525408645367278351L)
 final class StringBuilder(private val underlying: JavaStringBuilder)
-      extends Builder[Char, String]
+      extends Builder[Char, StringBuilder]
          with java.lang.CharSequence
          with IndexedSeq[Char]
-         with IndexedSeqOptimized[Char, IndexedSeq[Char]] {
+         with StringLike[StringBuilder] {
+
+  override protected[this] def thisCollection: StringBuilder = this
+  override protected[this] def toCollection(repr: StringBuilder): StringBuilder = repr
+
+  /** Creates a string builder buffer as builder for this class */
+  override protected[this] def newBuilder = new StringBuilder
 
   /** Constructs a string builder initialized with String initValue
    *  and with additional Char capacity initCapacity.
@@ -59,7 +66,7 @@ final class StringBuilder(private val underlying: JavaStringBuilder)
     arr
   }
 
-  def length: Int = underlying.length()
+  override def length: Int = underlying.length()
   def length_=(n: Int) { underlying.setLength(n) }
 
   /** Clears the builder contents.
@@ -105,7 +112,7 @@ final class StringBuilder(private val underlying: JavaStringBuilder)
 
   /** Equivalent to charAt.
    */
-  def apply(index: Int): Char = underlying charAt index
+  override def apply(index: Int): Char = underlying charAt index
 
   /** Removes the Char at the specified index.  The sequence is
    *  shortened by one.
@@ -428,6 +435,11 @@ final class StringBuilder(private val underlying: JavaStringBuilder)
    *  @return  the current contents of this sequence as a String
    */
   override def toString = underlying.toString
+  override def mkString = toString
 
-  def result(): String = toString
+  def result(): StringBuilder = this
 }
+
+object StringBuilder {
+  def newBuilder = new StringBuilder mapResult (_.toString)
+}
\ No newline at end of file
diff --git a/test/files/run/stringbuilder-drop.scala b/test/files/run/stringbuilder-drop.scala
new file mode 100644
index 0000000000..a9e5a71762
--- /dev/null
+++ b/test/files/run/stringbuilder-drop.scala
@@ -0,0 +1,7 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    val s = (new StringBuilder ++= "hello world") dropRight 1 toString;
+    assert(s == "hello worl")
+  }
+}
+