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https://issues.apache.org/jira/browse/SPARK-45610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17777405#comment-17777405
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Sean R. Owen commented on SPARK-45610:
--------------------------------------
I think it's better to make big changes at major version boundaries. I'd expect
we support Scala 3 at some point for Spark 4.x. Therefore I think it'd be OK to
proceed with these changes now for 4.0.
> Handle "Auto-application to `()` is deprecated."
> ------------------------------------------------
>
> Key: SPARK-45610
> URL: https://issues.apache.org/jira/browse/SPARK-45610
> Project: Spark
> Issue Type: Sub-task
> Components: GraphX, MLlib, Spark Core, SQL, Structured Streaming
> Affects Versions: 4.0.0
> Reporter: Yang Jie
> Priority: Major
>
> For the following case, a compile warning will be issued in Scala 2.13：
>
> {code:java}
> Welcome to Scala 2.13.12 (OpenJDK 64-Bit Server VM, Java 17.0.8).
> Type in expressions for evaluation. Or try :help.
> scala> class Foo {
> | def isEmpty(): Boolean = true
> | def isTrue(x: Boolean): Boolean = x
> | }
> class Foo
> scala> val foo = new Foo
> val foo: Foo = Foo@7061622
> scala> val ret = foo.isEmpty
> ^
> warning: Auto-application to `()` is deprecated. Supply the empty
> argument list `()` explicitly to invoke method isEmpty,
> or remove the empty argument list from its definition (Java-defined
> methods are exempt).
> In Scala 3, an unapplied method like this will be eta-expanded into a
> function. [quickfixable]
> val ret: Boolean = true {code}
> But for Scala 3, it is a compile error:
> {code:java}
> Welcome to Scala 3.3.1 (17.0.8, Java OpenJDK 64-Bit Server VM).
> Type in expressions for evaluation. Or try :help.
>
>
>
>
> scala> class Foo {
> | def isEmpty(): Boolean = true
> | def isTrue(x: Boolean): Boolean = x
> | }
> // defined class Foo
>
>
>
>
> scala> val foo = new Foo
> val foo: Foo = Foo@591f6f83
>
>
>
>
> scala> val ret = foo.isEmpty
> -- [E100] Syntax Error:
> --------------------------------------------------------
> 1 |val ret = foo.isEmpty
> | ^^^^^^^^^^^
> | method isEmpty in class Foo must be called with () argument
> |
> | longer explanation available when compiling with `-explain`
> 1 error found {code}
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