1 files changed, 36 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Concatable.java b/src/main/java/com/google/devtools/build/lib/syntax/Concatable.java
new file mode 100644
index 0000000000..81f489f7bf
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Concatable.java
@@ -0,0 +1,36 @@
+// Copyright 2016 The Bazel Authors. All Rights Reserved.
+//
+// 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 com.google.devtools.build.lib.syntax;
+
+import com.google.devtools.build.lib.events.Location;
+import javax.annotation.Nullable;
+
+/**
+ * Skylark values that support '+' operator should implement this interface.
+ */
+public interface Concatable {
+
+  /**
+   * Implements 'plus' operator on ClassObjects.
+   */
+  interface Concatter {
+    Concatable concat(Concatable lval, Concatable rval, Location loc) throws EvalException;
+  }
+
+  /* Returns a concatter for this {@link Concatable}.
+   * Two {@link Concatable}s can be added together if their concatters are equal.
+   */
+  @Nullable
+  Concatter getConcatter();
+}