Github user mike-jumper commented on a diff in the pull request:
https://github.com/apache/incubator-guacamole-client/pull/184#discussion_r134061382
--- Diff:
guacamole-ext/src/main/java/org/apache/guacamole/net/event/listener/Listener.java
---
@@ -0,0 +1,28 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.guacamole.net.event.listener;
+
+/**
+ * A marker interface extended by all listener types. This interface is
used
--- End diff --
I would fall on the "marker interface is an anti-pattern" side of the
fence. If there is no shared functional interface between these listeners, then
we shouldn't be defining a contract which states that there is.
That said, if it feels wrong to not have some common ancestor, then perhaps
there *should* be a shared functional interface? At the moment, the only
barrier I see preventing a common function for handling events is the variation
on whether a handler is `void` or `boolean`, but there may be a better approach
than the way things were done in the early guac days. Doing so would simplify
the way these events get fired, and would avoid all the `instanceof` checks and
casting.
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