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  1. Flink
  2. FLINK-5826

UDF/UDTF should support variable types and variable arguments


    • Type: Improvement
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 1.3.0
    • Component/s: None
    • Labels:


      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

      public class SimpleUDF extends ScalarFunction {
      	public int eval(Object... args) {
      		// do something

      for example 2, in Scala

      class SimpleUDF extends ScalarFunction {
        def eval(args: Any*): Int = {
          // do something

      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.

      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:?]

      The reason is that Scala will do a sugary modification to the signature of the method. The mothod

       def eval(args: Any*)

      will become

      def eval(args: scala.collection.Seq<Any>)

      in the class file.

      The code generation has been done in Java. If we use java style

      eval(Object... args)

      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?




            • Assignee:
              clarkyzl Zhuoluo Yang
              clarkyzl Zhuoluo Yang
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