Merge pull request #1304 from paulp/topic/empty-array-optimization

Topic/empty array optimization

13 files changed, 83 insertions, 6 deletions

diff --git a/src/compiler/scala/tools/cmd/gen/AnyVals.scala b/src/compiler/scala/tools/cmd/gen/AnyVals.scala
index 910804245b..b4f5641b98 100644
--- a/src/compiler/scala/tools/cmd/gen/AnyVals.scala
+++ b/src/compiler/scala/tools/cmd/gen/AnyVals.scala
@@ -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 440e546f19..d7311078ab 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 df0d2c73b1..02ef913fc5 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 1fa0c0d9e8..5a1bf16f1d 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 f058d7c26b..7bebbf9418 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 d942acec23..79ed2ac20b 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 ae36413469..fa2f9a97e7 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 4ee9383c2a..94204e893c 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 35c5fe3ff0..aef8608d2e 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/src/reflect/scala/tools/nsc/io/VirtualFile.scala b/src/reflect/scala/tools/nsc/io/VirtualFile.scala
index be888e92e6..9061534edc 100644
--- a/src/reflect/scala/tools/nsc/io/VirtualFile.scala
+++ b/src/reflect/scala/tools/nsc/io/VirtualFile.scala
@@ -33,7 +33,7 @@ class VirtualFile(val name: String, override val path: String) extends AbstractF
 
   //########################################################################
   // Private data
-  private var content = new Array[Byte](0)
+  private var content = Byte.emptyArray
 
   //########################################################################
   // Public Methods
diff --git a/src/reflect/scala/tools/nsc/io/ZipArchive.scala b/src/reflect/scala/tools/nsc/io/ZipArchive.scala
index d7ec209525..9d9d9a46f2 100644
--- a/src/reflect/scala/tools/nsc/io/ZipArchive.scala
+++ b/src/reflect/scala/tools/nsc/io/ZipArchive.scala
@@ -177,7 +177,7 @@ final class URLZipArchive(val url: URL) extends ZipArchive(null) {
       class FileEntry() extends Entry(zipEntry.getName) {
         override val toByteArray: Array[Byte] = {
           val len    = zipEntry.getSize().toInt
-          val arr    = new Array[Byte](len)
+          val arr    = if (len == 0) Byte.emptyArray else new Array[Byte](len)
           var offset = 0
 
           def loop() {
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
+  }
+}