Protocol Buffer runtime library and 'protoc' plugin

lib/protobuf/runtime/Extension.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/**
+ * An object representing an extension field.
+ */
+class Extension extends FieldInfo {
+
+  final String extendee;
+
+  Extension(String this.extendee, String name, int tagNumber, int fieldType,
+    [MakeDefaultFunc makeDefault, CreateBuilderFunc subBuilder = null,
+     ValueOfFunc valueOf = null]) :
+     super(name, tagNumber, fieldType, makeDefault, subBuilder, valueOf);
+
+  int hashCode() => extendee.hashCode() * 31 + tagNumber;
+
+  bool operator ==(Extension o) {
+    if (o is! Extension) {
+      return false;
+    }
+    return extendee == o.extendee && tagNumber == o.tagNumber;
+  }
+}
+