twalthr commented on a change in pull request #18352:
URL: https://github.com/apache/flink/pull/18352#discussion_r784653224
##########
File path:
flink-table/flink-table-common/src/main/java/org/apache/flink/table/functions/UserDefinedFunctionHelper.java
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@@ -243,6 +244,36 @@ public static void prepareInstance(ReadableConfig config,
UserDefinedFunction fu
cleanFunction(config, function);
}
+ /**
+ * Returns whether a {@link UserDefinedFunction} can be easily serialized
and identified by only
+ * a fully qualified class name. It must have a default constructor and no
serializable fields.
+ */
+ public static boolean isClassNameSerializable(UserDefinedFunction
function) {
+ final Class<?> functionClass = function.getClass();
+ if (!InstantiationUtil.hasPublicNullaryConstructor(functionClass)) {
+ // function must be parameterized
+ return false;
+ }
+ Class<?> currentClass = functionClass;
+ while (!currentClass.equals(UserDefinedFunction.class)) {
+ for (Field field : currentClass.getDeclaredFields()) {
+ if (!Modifier.isTransient(field.getModifiers())
+ && !Modifier.isStatic(field.getModifiers())) {
+ // function seems to be stateful
+ return false;
+ }
+ }
+ currentClass = currentClass.getSuperclass();
+ }
Review comment:
I'm also against magic but in this case the magic is minimal. It only
influences a plan digest and makes it more deterministic. Most users don't
parameterize their functions anyway and/or register it under a name which makes
them non-anonymous anyway.
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