Added constant empty array to the companion objects.

Because there are lots of times when you just need an
array and shouldn't have to allocate one every time or
pick a random spot to cache yet another empty array.

11 files changed, 84 insertions, 7 deletions

diff --git a/src/compiler/scala/tools/cmd/gen/AnyVals.scala b/src/compiler/scala/tools/cmd/gen/AnyVals.scala
index 7842603af7..3f8283590c 100644
--- a/src/compiler/scala/tools/cmd/gen/AnyVals.scala
+++ b/src/compiler/scala/tools/cmd/gen/AnyVals.scala
@@ -14,7 +14,7 @@ trait AnyValReps {
   sealed abstract class AnyValNum(name: String, repr: Option[String], javaEquiv: String) extends AnyValRep(name,repr,javaEquiv) {
 
     case class Op(val op : String, val doc : String)
-    
+
     private def companionCoercions(tos: AnyValRep*) = {
       tos.toList map (to =>
         """implicit def @javaequiv@2%s(x: @name@): %s = x.to%s""".format(to.javaEquiv, to.name, to.name)
@@ -24,7 +24,7 @@ trait AnyValReps {
     def coercionComment = """
   /** Language mandated coercions from @name@ to "wider" types.%s
    */""".format(coercionCommentExtra)
-    
+
     def implicitCoercions: List[String] = {
       val coercions = this match {
         case B     => companionCoercions(S, I, L, F, D)
@@ -247,7 +247,7 @@ trait AnyValReps {
     def classDoc  = interpolate(classDocTemplate)
     def objectDoc = ""
     def mkImports = ""
-    
+
     def mkClass       = assemble("final abstract class " + name + " private extends AnyVal", classLines)
     def mkObject      = assemble("object " + name + " extends AnyValCompanion", objectLines)
     def make()    = List[String](
@@ -320,7 +320,13 @@ def unbox(x: java.lang.Object): @name@ = @unboxImpl@
 override def toString = "object scala.@name@"
 """
 
-  def nonUnitCompanions = ""  // todo
+  def nonUnitCompanions = """
+/** A highly reusable empty array, useful for avoiding
+ *  allocations when you need one.
+ *
+ *  @return     a constant 0-length Array[@name@]
+ */
+final val emptyArray = new Array[@name@](0)"""
 
   def cardinalCompanion = """
 /** The smallest value representable as a @name@.
@@ -341,9 +347,6 @@ final val NaN              = @boxed@.NaN
 final val PositiveInfinity = @boxed@.POSITIVE_INFINITY
 final val NegativeInfinity = @boxed@.NEGATIVE_INFINITY
 
-@deprecated("use @name@.MinPositiveValue instead", "2.9.0")
-final val Epsilon  = MinPositiveValue
-
 /** The negative number with the greatest (finite) absolute value which is representable
  *  by a @name@.  Note that it differs from [[java.lang.@name@.MIN_VALUE]], which
  *  is the smallest positive value representable by a @name@.  In Scala that number
diff --git a/src/library/scala/Boolean.scala b/src/library/scala/Boolean.scala
index 014928d986..617c2eac36 100644
--- a/src/library/scala/Boolean.scala
+++ b/src/library/scala/Boolean.scala
@@ -135,5 +135,12 @@ object Boolean extends AnyValCompanion {
    */
   override def toString = "object scala.Boolean"
 
+
+  /** A highly reusable empty array, useful for avoiding
+   *  allocations when you need one.
+   *
+   *  @return     a constant 0-length Array[Boolean]
+   */
+  final val emptyArray = new Array[Boolean](0)
 }
 
diff --git a/src/library/scala/Byte.scala b/src/library/scala/Byte.scala
index 6f54f6cedf..7a5a36c5f6 100644
--- a/src/library/scala/Byte.scala
+++ b/src/library/scala/Byte.scala
@@ -625,6 +625,14 @@ object Byte extends AnyValCompanion {
    */
   override def toString = "object scala.Byte"
 
+
+  /** A highly reusable empty array, useful for avoiding
+   *  allocations when you need one.
+   *
+   *  @return     a constant 0-length Array[Byte]
+   */
+  final val emptyArray = new Array[Byte](0)
+  
   /** Language mandated coercions from Byte to "wider" types.
    */
   implicit def byte2short(x: Byte): Short = x.toShort
diff --git a/src/library/scala/Char.scala b/src/library/scala/Char.scala
index b681ae1693..5b0caf327f 100644
--- a/src/library/scala/Char.scala
+++ b/src/library/scala/Char.scala
@@ -625,6 +625,14 @@ object Char extends AnyValCompanion {
    */
   override def toString = "object scala.Char"
 
+
+  /** A highly reusable empty array, useful for avoiding
+   *  allocations when you need one.
+   *
+   *  @return     a constant 0-length Array[Char]
+   */
+  final val emptyArray = new Array[Char](0)
+  
   /** Language mandated coercions from Char to "wider" types.
    */
   implicit def char2int(x: Char): Int = x.toInt
diff --git a/src/library/scala/Double.scala b/src/library/scala/Double.scala
index 510de92a2a..09b393e515 100644
--- a/src/library/scala/Double.scala
+++ b/src/library/scala/Double.scala
@@ -400,5 +400,13 @@ object Double extends AnyValCompanion {
   /** The String representation of the scala.Double companion object.
    */
   override def toString = "object scala.Double"
+
+
+  /** A highly reusable empty array, useful for avoiding
+   *  allocations when you need one.
+   *
+   *  @return     a constant 0-length Array[Double]
+   */
+  final val emptyArray = new Array[Double](0)
 }
 
diff --git a/src/library/scala/Float.scala b/src/library/scala/Float.scala
index b9c116da0b..4aa74244b0 100644
--- a/src/library/scala/Float.scala
+++ b/src/library/scala/Float.scala
@@ -401,6 +401,14 @@ object Float extends AnyValCompanion {
    */
   override def toString = "object scala.Float"
 
+
+  /** A highly reusable empty array, useful for avoiding
+   *  allocations when you need one.
+   *
+   *  @return     a constant 0-length Array[Float]
+   */
+  final val emptyArray = new Array[Float](0)
+  
   /** Language mandated coercions from Float to "wider" types.
    */
   implicit def float2double(x: Float): Double = x.toDouble
diff --git a/src/library/scala/Int.scala b/src/library/scala/Int.scala
index b2a4f93253..8f05596633 100644
--- a/src/library/scala/Int.scala
+++ b/src/library/scala/Int.scala
@@ -625,6 +625,14 @@ object Int extends AnyValCompanion {
    */
   override def toString = "object scala.Int"
 
+
+  /** A highly reusable empty array, useful for avoiding
+   *  allocations when you need one.
+   *
+   *  @return     a constant 0-length Array[Int]
+   */
+  final val emptyArray = new Array[Int](0)
+  
   /** Language mandated coercions from Int to "wider" types.
    */
   implicit def int2long(x: Int): Long = x.toLong
diff --git a/src/library/scala/Long.scala b/src/library/scala/Long.scala
index 40932a65a7..7447fa3a15 100644
--- a/src/library/scala/Long.scala
+++ b/src/library/scala/Long.scala
@@ -625,6 +625,14 @@ object Long extends AnyValCompanion {
    */
   override def toString = "object scala.Long"
 
+
+  /** A highly reusable empty array, useful for avoiding
+   *  allocations when you need one.
+   *
+   *  @return     a constant 0-length Array[Long]
+   */
+  final val emptyArray = new Array[Long](0)
+  
   /** Language mandated coercions from Long to "wider" types.
    */
   implicit def long2float(x: Long): Float = x.toFloat
diff --git a/src/library/scala/Short.scala b/src/library/scala/Short.scala
index 687b198a11..af7eb699d8 100644
--- a/src/library/scala/Short.scala
+++ b/src/library/scala/Short.scala
@@ -625,6 +625,14 @@ object Short extends AnyValCompanion {
    */
   override def toString = "object scala.Short"
 
+
+  /** A highly reusable empty array, useful for avoiding
+   *  allocations when you need one.
+   *
+   *  @return     a constant 0-length Array[Short]
+   */
+  final val emptyArray = new Array[Short](0)
+  
   /** Language mandated coercions from Short to "wider" types.
    */
   implicit def short2int(x: Short): Int = x.toInt
diff --git a/test/files/run/empty-array.check b/test/files/run/empty-array.check
new file mode 100644
index 0000000000..bb0b1cf658
--- /dev/null
+++ b/test/files/run/empty-array.check
@@ -0,0 +1,3 @@
+0
+0
+0
diff --git a/test/files/run/empty-array.scala b/test/files/run/empty-array.scala
new file mode 100644
index 0000000000..e56c86df5c
--- /dev/null
+++ b/test/files/run/empty-array.scala
@@ -0,0 +1,8 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    println(Byte.emptyArray.length)
+    println(Double.emptyArray.length)
+    println(Boolean.emptyArray.length)
+    // okay okay okay
+  }
+}