[jira] [Commented] (GROOVY-8580) CLONE - Support `var` keyword of Java10 (finalise behavior of keyword under @CompileStatic)

["mgroovy (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/GROOVY-8580?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17037282#comment-17037282 ] 

mgroovy commented on GROOVY-8580:
---------------------------------

* If this has not yet been decided, I have one more (very practical) point to add to the (admittedly imho stronger) points I tried to malke on the mailing list:
 * I use a lot of @CompileStatic and code which looks like (I use final here of course, but the same argument goes of course for var):
{code:java}
final t = createPersonTable() // returns PersonTable instance which is a Table
final foreignId = retrieveForeignId(t) // <T extends Table> Number retrieveForeignId(T t)
{code}

 * Code like that often does not compile under @CompileStatic, if retrieveForeignId is a method taking a generic argument, since the type of t is Object, and the compiler (incorrectly) rejects the call
 * If I give the type of t explicitly as PersonTable then the code compiles
 * This is evidently something that could be fixed in the @CompileStatic parts of Groovy, but I guess the effort for that would be high, since it ionvolves generics
 * If, however, the type of t would be PersonTable as I suggest final/var should behave, then (as an added benefit to all the others) this problem could be avoided

> CLONE - Support `var` keyword of Java10 (finalise behavior of keyword under @CompileStatic)
> -------------------------------------------------------------------------------------------
>
>                 Key: GROOVY-8580
>                 URL: https://issues.apache.org/jira/browse/GROOVY-8580
>             Project: Groovy
>          Issue Type: New Feature
>            Reporter: Daniel Sun
>            Priority: Blocker
>             Fix For: 4.x
>
>
> As part of GROOVY-8498 there is now support for the {{var}} keyword to provide compatibility with:
> http://openjdk.java.net/jeps/286 (Java 10)
> http://openjdk.java.net/jeps/323 (targeted for Java 11)
> For dynamic Groovy, {{var}} is an alias for {{def}}. Under {{@CompileStatic}}, there are three fairly obvious potential behaviors that could make sense for Groovy:
> * a direct alias for {{def}} in which case normal Groovy flow typing would apply (this is currently what is implemented but is more flexible than what Java developers might expect)
> * similar to the alias for {{def}} in that it allows the inferred type to change as further instructions are executed but it would only be allowed to change to sub-types of the initially inferred type (needs further investigation but if possible would combine some of the nice aspects of Groovy def and Java var behavior)
> * a direct equivalent of Java (this would be the most work and would differ greatly from Groovy behavior and in general would be hard to marry up with Groovy semantics)
> We need to finalize the behavior we want before releasing non-alpha versions of Groovy 3.



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