[jira] [Commented] (GROOVY-10943) Consider additional use of _ as a placeholder

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

    [ https://issues.apache.org/jira/browse/GROOVY-10943?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17692374#comment-17692374 ] 

Eric Milles commented on GROOVY-10943:
--------------------------------------

In case of Groovy multiple-assignment, you can leave off unused trailing components:
{code:groovy}
def (coordX, coordY) = coord3D()
{code}

Is this change necessary for Record pattern matching or something like that?

> Consider additional use of _ as a placeholder
> ---------------------------------------------
>
>                 Key: GROOVY-10943
>                 URL: https://issues.apache.org/jira/browse/GROOVY-10943
>             Project: Groovy
>          Issue Type: Improvement
>            Reporter: Paul King
>            Priority: Major
>              Labels: GEP
>
> Recent Java versions make underscore, "_", an illegal variable name. This is to allow it to be used as a placeholder as per JEP 302: Lambda Leftovers[1]. This issue is to explore how better to have such a placeholder in Groovy.
> This strengthens an informal convention already in use. Instead of writing this:
> {code}
> def (coordX, coordY, unusedZ) = coord3D()
> {code}
> Sometimes it is written as:
> {code}
> def (coordX, coordY, _) = coord3D()
> {code}
> Currently, the underscore is a variable and could be used but the convention is that
> it would be ignored.
> This convention doesn't scale if more than one result is to be ignored (here a double underscore is used for the second ignored result):
> {code}
> def (coordX, coordY, _, __) = coord3DwithColor()
> {code}
> This idea being that the following should be valid:
> {code}
> def (coordX, coordY, _, _) = coord3DwithColor()
> {code}
> Which currently gives an error for the duplicated variable name.
> Similarly, the idea is applicable for lambda parameters (as per the example in the previously mentioned Java JEP):
> {code}
> BiFunction<Integer, String, String> biss = (i, _) -> String.valueOf(i)
> {code}
> We could follow Java's lead and make underscore an invalid variable name but it might be possible to keep uses of that name except where there is more than one occurrence of the name. In such a circumstance, use of the name would no longer reference a variable. We need to check the impacts of shadowing as per discussions in the JEP.
>  [1] [https://openjdk.org/jeps/302]
>  



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