[jira] [Created] (FLINK-14380) Type Extractor POJO setter check does not allow for Immutable Case Class

[Shang Yuanchun (Jira)]

Elliot Pourmand created FLINK-14380:
---------------------------------------

             Summary: Type Extractor POJO setter check does not allow for Immutable Case Class
                 Key: FLINK-14380
                 URL: https://issues.apache.org/jira/browse/FLINK-14380
             Project: Flink
          Issue Type: Bug
          Components: API / Scala
    Affects Versions: 1.9.0, 1.8.2
         Environment: Not relavent

 
            Reporter: Elliot Pourmand


When deciding if a class conforms to POJO using the type extractor Flink checks that the class implements a setter and getter method. For the setter method Flink makes the assertion that the return type is `Void`. This is an issue if using a case class as often the return type of a case class setter is a copy of the objects class. Consider the following case class:

```scala
case class  SomeClass(x: Int) {
    x_=(newX: Int): SomeClass = { this.copy(x = newX) }
}
```

This class will be identified as not being valid POJO although getter (generated) and setter methods are provided because the return type of the setter is not void.

This issue discourages immutabilaty and makes the usage of case classes not possible without falling back to Kryo Serializer.

The issue is located in https://github.com/apache/flink/blob/master/flink-core/src/main/java/org/apache/flink/api/java/typeutils/TypeExtractor.java on line 1806. Here is a permalink to the line

https://github.com/apache/flink/blob/80b27a150026b7b5cb707bd9fa3e17f565bb8112/flink-core/src/main/java/org/apache/flink/api/java/typeutils/TypeExtractor.java#L1806


A copy of the if check is here
```
if((methodNameLow.equals("set"+fieldNameLow) || methodNameLow.equals(fieldNameLow+"_$eq")) &&
                                        m.getParameterTypes().length == 1 && // one parameter of the field's type
                                        (m.getGenericParameterTypes()[0].equals( fieldType ) || (fieldTypeWrapper != null && m.getParameterTypes()[0].equals( fieldTypeWrapper )) || (fieldTypeGeneric != null && m.getGenericParameterTypes()[0].equals(fieldTypeGeneric) ) )&&
                                        // return type is void.
                                        m.getReturnType().equals(Void.TYPE)
                                ) {
                                        hasSetter = true;
                                }
                        }
```

I believe the `m.getReturnType().equals(Void.TYPE)` should be modified to
`m.getReturnType().equals(Void.TYPE) || m.getReturnType().equals(class.Type)`

This will allow for case class setters which return copies of the object enabling to use case classes.



--
This message was sent by Atlassian Jira
(v8.3.4#803005)