Elliot Pourmand created FLINK-14380:
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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.
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