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https://issues.apache.org/jira/browse/FLINK-4883?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15651101#comment-15651101
]
ASF GitHub Bot commented on FLINK-4883:
---------------------------------------
Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/2729#discussion_r87201177
--- Diff:
flink-java/src/main/java/org/apache/flink/api/java/ScalaObjectChecker.java ---
@@ -0,0 +1,51 @@
+/*
+ * 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.flink.api.java;
+
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.api.common.InvalidProgramException;
+
+/**
+ * Scala Object checker tries to verify if a class is implemented by
+ * Scala Object
+ */
+@Internal
+public class ScalaObjectChecker {
+ public static boolean isPotentialScalaObject(Object o) {
--- End diff --
I think there might be a nicer/idiomatic way of doing this check through:
```
def isSingleton[A](a: A)(implicit ev: A <:< Singleton = null) =
Option(ev).isDefined
```
> Prevent UDFs implementations through Scala singleton objects
> ------------------------------------------------------------
>
> Key: FLINK-4883
> URL: https://issues.apache.org/jira/browse/FLINK-4883
> Project: Flink
> Issue Type: Bug
> Reporter: Stefan Richter
> Assignee: Renkai Ge
>
> Currently, user can create and use UDFs in Scala like this:
> {code}
> object FlatMapper extends RichCoFlatMapFunction[Long, String, (Long, String)]
> {
> ...
> }
> {code}
> However, this leads to problems as the UDF is now a singleton that Flink
> could use across several operator instances, which leads to job failures. We
> should detect and prevent the usage of singleton UDFs.
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