1 files changed, 43 insertions, 0 deletions
diff --git a/kamon-core/src/legacy-main/scala/kamon/util/MapMerge.scala b/kamon-core/src/legacy-main/scala/kamon/util/MapMerge.scala
new file mode 100644
index 00000000..6fc6fb15
--- /dev/null
+++ b/kamon-core/src/legacy-main/scala/kamon/util/MapMerge.scala
@@ -0,0 +1,43 @@
+/*
+ * =========================================================================================
+ * Copyright © 2013-2015 the kamon project <http://kamon.io/>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ * =========================================================================================
+ */
+
+package kamon.util
+
+object MapMerge {
+
+  /**
+   *  Merge two immutable maps with the same key and value types, using the provided valueMerge function.
+   */
+  implicit class Syntax[K, V](val map: Map[K, V]) extends AnyVal {
+    def merge(that: Map[K, V], valueMerge: (V, V) ⇒ V): Map[K, V] = {
+      val merged = Map.newBuilder[K, V]
+
+      map.foreach {
+        case (key, value) ⇒
+          val mergedValue = that.get(key).map(v ⇒ valueMerge(value, v)).getOrElse(value)
+          merged += key → mergedValue
+      }
+
+      that.foreach {
+        case kv @ (key, _) if !map.contains(key) ⇒ merged += kv
+        case other                               ⇒ // ignore, already included.
+      }
+
+      merged.result();
+    }
+  }
+
+}