1 files changed, 35 insertions, 5 deletions
diff --git a/kamon-core/src/main/scala/kamon/metric/instrument/UnitOfMeasurement.scala b/kamon-core/src/main/scala/kamon/metric/instrument/UnitOfMeasurement.scala
index c5a1b81a..5952b906 100644
--- a/kamon-core/src/main/scala/kamon/metric/instrument/UnitOfMeasurement.scala
+++ b/kamon-core/src/main/scala/kamon/metric/instrument/UnitOfMeasurement.scala
@@ -22,14 +22,27 @@ package kamon.metric.instrument
  *  recorders and might be used to scale certain kinds of measurements in metric backends.
  */
 trait UnitOfMeasurement {
+  type U <: UnitOfMeasurement
+
   def name: String
   def label: String
+  def scale(toUnit: U)(value: Double): Double = value
+
+  def tryScale(toUnit: UnitOfMeasurement)(value: Double): Double =
+    if (canScale(toUnit)) scale(toUnit.asInstanceOf[U])(value)
+    else throw new IllegalArgumentException(s"Can't scale different types of units `$name` and `${toUnit.name}`")
+
+  protected def canScale(toUnit: UnitOfMeasurement): Boolean
+
 }
 
 object UnitOfMeasurement {
   case object Unknown extends UnitOfMeasurement {
+    override type U = Unknown.type
     val name = "unknown"
     val label = "unknown"
+
+    override protected def canScale(toUnit: UnitOfMeasurement): Boolean = UnitOfMeasurement.isUnknown(toUnit)
   }
 
   def isUnknown(uom: UnitOfMeasurement): Boolean =
@@ -47,10 +60,13 @@ object UnitOfMeasurement {
  *  UnitOfMeasurement representing time.
  */
 case class Time(factor: Double, label: String) extends UnitOfMeasurement {
+  override type U = Time
   val name = "time"
 
-  def scale(toUnit: Time)(value: Double): Double =
+  override def scale(toUnit: Time)(value: Double): Double =
     (value * factor) / toUnit.factor
+
+  override protected def canScale(toUnit: UnitOfMeasurement): Boolean = UnitOfMeasurement.isTime(toUnit)
 }
 
 object Time {
@@ -58,22 +74,36 @@ object Time {
   val Microseconds = Time(1E-6, "µs")
   val Milliseconds = Time(1E-3, "ms")
   val Seconds = Time(1, "s")
+
+  val units = List(Nanoseconds, Microseconds, Milliseconds, Seconds)
+
+  def apply(time: String): Time = units.find(_.label.toLowerCase == time.toLowerCase) getOrElse {
+    throw new IllegalArgumentException(s"Can't recognize time unit '$time'")
+  }
 }
 
 /**
  *  UnitOfMeasurement representing computer memory space.
  */
 case class Memory(factor: Double, label: String) extends UnitOfMeasurement {
+  override type U = Memory
   val name = "bytes"
 
-  def scale(toUnit: Memory)(value: Double): Double =
+  override def scale(toUnit: Memory)(value: Double): Double =
     (value * factor) / toUnit.factor
+
+  override protected def canScale(toUnit: UnitOfMeasurement): Boolean = UnitOfMeasurement.isMemory(toUnit)
 }
 
 object Memory {
   val Bytes = Memory(1, "b")
   val KiloBytes = Memory(1024, "Kb")
-  val MegaBytes = Memory(1024E2, "Mb")
-  val GigaBytes = Memory(1024E3, "Gb")
-}
+  val MegaBytes = Memory(1024 * 1024, "Mb")
+  val GigaBytes = Memory(1024 * 1024 * 1024, "Gb")
 
+  val units = List(Bytes, KiloBytes, MegaBytes, GigaBytes)
+
+  def apply(memory: String): Memory = units.find(_.label.toLowerCase == memory.toLowerCase) getOrElse {
+    throw new IllegalArgumentException(s"Can't recognize memory unit '$memory'")
+  }
+}