1 files changed, 50 insertions, 0 deletions
diff --git a/kamon-core/src/main/scala/kamon/tag/Tag.scala b/kamon-core/src/main/scala/kamon/tag/Tag.scala
new file mode 100644
index 00000000..69a5d7e7
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/tag/Tag.scala
@@ -0,0 +1,50 @@
+package kamon.tag
+
+import java.lang.{Boolean => JBoolean, Long => JLong, String => JString}
+
+/**
+  * Marker trait for allowed Tag implementations. Users are not meant to create implementations of this trait outside
+  * of Kamon. Furthermore, users of TagSet might never need to interact with these classes but rather perform lookups
+  * using the lookup DSL.
+  */
+sealed trait Tag {
+  def key: JString
+}
+
+object Tag {
+
+  /**
+    * Represents a String key pointing to a String value.
+    */
+  trait String extends Tag {
+    def value: JString
+  }
+
+
+  /**
+    * Represents a String key pointing to a Boolean value.
+    */
+  trait Boolean extends Tag {
+    def value: JBoolean
+  }
+
+
+  /**
+    * Represents a String key pointing to a Long value.
+    */
+  trait Long extends Tag {
+    def value: JLong
+  }
+
+
+  /**
+    * Returns the value held inside of a Tag instance. This utility function is specially useful when iterating over
+    * tags but not caring about the concrete tag type.
+    */
+  def unwrapValue(tag: Tag): Any = tag match {
+    case t: Tag.String  => t.value
+    case t: Tag.Boolean => t.value
+    case t: Tag.Long    => t.value
+  }
+}
+