[jira] [Created] (FLINK-5826) UDF/UDTF should support variable types and variable arguments

["Zhuoluo Yang (JIRA)" <ji...@apache.org>]

Zhuoluo Yang created FLINK-5826:
-----------------------------------

             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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