Merge pull request #667 from Dwolla/TraceableValue

add TraceableValue typeclass and base implementations

modules/core/shared/src/main/scala/TraceValue.scala

@@ -14,11 +14,47 @@ object TraceValue {
   case class BooleanValue(value: Boolean) extends TraceValue
   case class NumberValue(value: Number) extends TraceValue
 
-  implicit def stringToTraceValue(value: String): TraceValue = StringValue(value)
-  implicit def boolToTraceValue(value: Boolean): TraceValue = BooleanValue(value)
-  implicit def intToTraceValue(value: Int): TraceValue = NumberValue(value)
-  implicit def longToTraceValue(value: Long): TraceValue = NumberValue(value)
-  implicit def floatToTraceValue(value: Float): TraceValue = NumberValue(value)
-  implicit def doubleToTraceValue(value: Double): TraceValue = NumberValue(value)
+  implicit def viaTraceableValue[A: TraceableValue](a: A): TraceValue =
+    TraceableValue[A].toTraceValue(a)
 
+  @deprecated("use toTraceValue", "0.3.0")
+  def stringToTraceValue(value: String): TraceValue = StringValue(value)
+  @deprecated("use toTraceValue", "0.3.0")
+  def boolToTraceValue(value: Boolean): TraceValue = BooleanValue(value)
+  @deprecated("use toTraceValue", "0.3.0")
+  def intToTraceValue(value: Int): TraceValue = NumberValue(value)
+  @deprecated("use toTraceValue", "0.3.0")
+  def longToTraceValue(value: Long): TraceValue = NumberValue(value)
+  @deprecated("use toTraceValue", "0.3.0")
+  def floatToTraceValue(value: Float): TraceValue = NumberValue(value)
+  @deprecated("use toTraceValue", "0.3.0")
+  def doubleToTraceValue(value: Double): TraceValue = NumberValue(value)
+}
+
+/** A lawless typeclass responsible for converting a value of the type
+  * parameter `A` to Natchez's `TraceValue`.
+  *
+  * You may want to use this to customize the formatting of a value
+  * before attaching it to a span, or to support adding tracing as a
+  * cross-cutting concern using aspect-oriented programming from a
+  * library such as cats-tagless.
+  *
+  * @tparam A The type to be converted to `TraceValue`
+  */
+trait TraceableValue[A] { outer =>
+  def toTraceValue(a: A): TraceValue
+
+  final def contramap[B](f: B => A): TraceableValue[B] =
+    (b: B) => outer.toTraceValue(f(b))
+}
+
+object TraceableValue {
+  def apply[A: TraceableValue]: TraceableValue[A] = implicitly
+
+  implicit val stringToTraceValue: TraceableValue[String] = TraceValue.StringValue(_)
+  implicit val booleanToTraceValue: TraceableValue[Boolean] = TraceValue.BooleanValue(_)
+  implicit val intToTraceValue: TraceableValue[Int] = TraceValue.NumberValue(_)
+  implicit val longToTraceValue: TraceableValue[Long] = TraceValue.NumberValue(_)
+  implicit val doubleToTraceValue: TraceableValue[Double] = TraceValue.NumberValue(_)
+  implicit val floatToTraceValue: TraceableValue[Float] = TraceValue.NumberValue(_)
 }