Share instance of ClassTag in a ClassValue based cache

scala · Mar 15, 2019 · 3e621d2 · 3e621d2
1 parent 6f4ee4a
commit 3e621d2
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Showing 2 changed files with 33 additions and 16 deletions.
diff --git a/src/library/scala/reflect/ClassTag.scala b/src/library/scala/reflect/ClassTag.scala
@@ -121,29 +121,36 @@ object ClassTag {
   val Nothing : ClassTag[scala.Nothing]    = Manifest.Nothing
   val Null    : ClassTag[scala.Null]       = Manifest.Null
 
+  private[this] val cache = new ClassValue[ClassTag[_]] {
+    override def computeValue(runtimeClass: jClass[_]): ClassTag[_] = new GenericClassTag[AnyRef](runtimeClass)
+  }
+
   @SerialVersionUID(1L)
   private class GenericClassTag[T](val runtimeClass: jClass[_]) extends ClassTag[T] {
     override def newArray(len: Int): Array[T] = {
       java.lang.reflect.Array.newInstance(runtimeClass, len).asInstanceOf[Array[T]]
     }
   }
 
-  def apply[T](runtimeClass1: jClass[_]): ClassTag[T] =
-    runtimeClass1 match {
-      case java.lang.Byte.TYPE      => ClassTag.Byte.asInstanceOf[ClassTag[T]]
-      case java.lang.Short.TYPE     => ClassTag.Short.asInstanceOf[ClassTag[T]]
-      case java.lang.Character.TYPE => ClassTag.Char.asInstanceOf[ClassTag[T]]
-      case java.lang.Integer.TYPE   => ClassTag.Int.asInstanceOf[ClassTag[T]]
-      case java.lang.Long.TYPE      => ClassTag.Long.asInstanceOf[ClassTag[T]]
-      case java.lang.Float.TYPE     => ClassTag.Float.asInstanceOf[ClassTag[T]]
-      case java.lang.Double.TYPE    => ClassTag.Double.asInstanceOf[ClassTag[T]]
-      case java.lang.Boolean.TYPE   => ClassTag.Boolean.asInstanceOf[ClassTag[T]]
-      case java.lang.Void.TYPE      => ClassTag.Unit.asInstanceOf[ClassTag[T]]
-      case ObjectTYPE               => ClassTag.Object.asInstanceOf[ClassTag[T]]
-      case NothingTYPE              => ClassTag.Nothing.asInstanceOf[ClassTag[T]]
-      case NullTYPE                 => ClassTag.Null.asInstanceOf[ClassTag[T]]
-      case _                        => new GenericClassTag[T](runtimeClass1)
-    }
+  def apply[T](runtimeClass1: jClass[_]): ClassTag[T] = runtimeClass1 match {
+    case x if x.isPrimitive =>  primitiveClassTag(runtimeClass1)
+    case ObjectTYPE => ClassTag.Object.asInstanceOf[ClassTag[T]]
+    case NothingTYPE => ClassTag.Nothing.asInstanceOf[ClassTag[T]]
+    case NullTYPE => ClassTag.Null.asInstanceOf[ClassTag[T]]
+    case _ => cache.get(runtimeClass1).asInstanceOf[ClassTag[T]]
+  }
+
+  private def primitiveClassTag[T](runtimeClass1: Class[_]): ClassTag[T] = runtimeClass1 match {
+    case java.lang.Byte.TYPE => ClassTag.Byte.asInstanceOf[ClassTag[T]]
+    case java.lang.Short.TYPE => ClassTag.Short.asInstanceOf[ClassTag[T]]
+    case java.lang.Character.TYPE => ClassTag.Char.asInstanceOf[ClassTag[T]]
+    case java.lang.Integer.TYPE => ClassTag.Int.asInstanceOf[ClassTag[T]]
+    case java.lang.Long.TYPE => ClassTag.Long.asInstanceOf[ClassTag[T]]
+    case java.lang.Float.TYPE => ClassTag.Float.asInstanceOf[ClassTag[T]]
+    case java.lang.Double.TYPE => ClassTag.Double.asInstanceOf[ClassTag[T]]
+    case java.lang.Boolean.TYPE => ClassTag.Boolean.asInstanceOf[ClassTag[T]]
+    case java.lang.Void.TYPE => ClassTag.Unit.asInstanceOf[ClassTag[T]]
+  }
 
   def unapply[T](ctag: ClassTag[T]): Option[Class[_]] = Some(ctag.runtimeClass)
 }
diff --git a/test/files/run/classtags-cached.scala b/test/files/run/classtags-cached.scala
@@ -0,0 +1,10 @@
+import reflect.ClassTag
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    assert(implicitly[ClassTag[SomeClass]] eq implicitly[ClassTag[SomeClass]])
+    assert(implicitly[ClassTag[Array[SomeClass]]] eq implicitly[ClassTag[Array[SomeClass]]])
+  }
+}
+
+class SomeClass