[
https://issues.apache.org/jira/browse/FLINK-5826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15873947#comment-15873947
]
Zhuoluo Yang commented on FLINK-5826:
-------------------------------------
Thanks [~jark] , I'd like to do some test on this. It seems a concise design.
IMHO, a meaningful exception would also be useful to users if necessary. I will
try this annotation.
> 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?
--
This message was sent by Atlassian JIRA
(v6.3.15#6346)
