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https://issues.apache.org/jira/browse/FLINK-5964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15897342#comment-15897342
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Stephan Ewen commented on FLINK-5964:
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[~jayson.minard] Currently, Flink supports two different modes: Object
*reusing* and *non-reusing*.
The *non-reusing* mode is the default and should never try to create an object
just like that, but always as a result of a copy or deserialization. The
*reusing* mode can only work with mutable objects (by definition).
Can you explain a bit more where the clash with the immutable types happens?
> Change TypeSerializers to allow construction of immutable types
> ---------------------------------------------------------------
>
> Key: FLINK-5964
> URL: https://issues.apache.org/jira/browse/FLINK-5964
> Project: Flink
> Issue Type: Improvement
> Components: Core
> Affects Versions: 2.0.0, 1.1.4
> Reporter: Jayson Minard
> Priority: Minor
>
> If your programming language has a lot of Immutable types (and with no
> default constructor) Flink forces you to create new versions as read/write
> POJO otherwise the types are rejected by the system. In Kotlin for example,
> given a class and property values we can determine which constructor to call
> and invoke it using knowledge of default values, nullable types and which
> properties can be set in construction or after construction.
> Flink provides no opportunity to use this model because Serializers are
> littered with calls to `createInstance` that are not passed any values so
> have no opportunity to fully inflate the object on construction.
> This means that when you use Flink you throw away maybe hundreds of state
> objects (my worst case) and have to create Flink-only variations which
> becomes grunt work that adds no value.
> Currently TypeExtractor isn't extendable, and all of the special cases are
> hard coded. It should be configured the order of checking for type
> information so that pluggable types can be added into the chain of analysis.
> For example before `analyzePojo` is called I could special case a Kotlin
> class returning a different TypeInformation instance. But I don't think that
> solves the whole problem since other TypeSerializers make assumptions and
> call `createInstance` on other TypeSerializers without knowing how they would
> want to do the construction (in the Kotlin case it would be "tell me to
> construct my instance and give me the list of named fields and serializers to
> get their values and let me decide what to do).
> What is the best idea for this change? With guidance, I can work on the PR.
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