Zhuoluo Yang created FLINK-5826:
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Summary: UDF/UDTF should support variable types and variable arguments
Key: FLINK-5826
URL:
https://issues.apache.org/jira/browse/FLINK-5826 Project: Flink
Issue Type: Improvement
Reporter: Zhuoluo Yang
Assignee: Zhuoluo Yang
In some cases, UDF/UDTF should support variable types and variable arguments. Many UDF/UDTF developers wish to make the # of arguments and types flexible to users. They try to make their functions flexible.
Thus, we should support the following styles of UDF/UDTFs.
for example 1, in Java
{code:java}
public class SimpleUDF extends ScalarFunction {
public int eval(Object... args) {
// do something
}
}
{code}
for example 2, in Scala
{code}
class SimpleUDF extends ScalarFunction {
def eval(args: Any*): Int = {
// do something
}
}
{code}
If we modify the code in UserDefinedFunctionUtils.getSignature() and make both signatures pass. The first example will work normally. However, the second example will raise an exception.
{noformat}
Caused by: org.codehaus.commons.compiler.CompileException: Line 58, Column 0: No applicable constructor/method found for actual parameters "java.lang.String"; candidates are: "public java.lang.Object test.SimpleUDF.eval(scala.collection.Seq)"
at org.codehaus.janino.UnitCompiler.compileError(UnitCompiler.java:11523) ~[janino-3.0.6.jar:?]
at org.codehaus.janino.UnitCompiler.findMostSpecificIInvocable(UnitCompiler.java:8679) ~[janino-3.0.6.jar:?]
at org.codehaus.janino.UnitCompiler.findIMethod(UnitCompiler.java:8539) ~[janino-3.0.6.jar:?]
{noformat}
The reason is that Scala will do a sugary modification to the signature of the method. The mothod {code} def eval(args: Any*){code} will become {code}def eval(args: scala.collection.Seq<Any>){code} in the class file.
The code generation has been done in Java. If we use java style {code}eval(Object... args){code} to call the Scala method, it will raise the above exception.
However, I can't always restrict users to use Java to write a UDF/UDTF. Any ideas in variable types and variable arguments of Scala UDF/UDTFs to prevent the compilation failure?
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