[jira] [Comment Edited] (GROOVY-8826) Captured loop variables have surprising and Java-incompatible behavior

["Daniel Sun (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/GROOVY-8826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16640975#comment-16640975 ] 

Daniel Sun edited comment on GROOVY-8826 at 10/7/18 5:59 AM:
-------------------------------------------------------------

 Here is a workaround, but we should fix the issue at last...
{code:java}
import java.util.ArrayList;
import java.util.Arrays;

public class Test {
    public static void main(String... args) {
        ArrayList<Runnable> closures = new ArrayList<>();

        for (int i: new int[] {1, 2}) {
            int tmp = i
            closures.add(() -> System.out.println(tmp));
        }

        for (Runnable closure: closures)
            closure.run();
    }
}
{code}


was (Author: daniel_sun):
 Here is a workaround, but we should fix the issue at last...
{code:java}
import java.util.ArrayList;
import java.util.Arrays;

public class Test {
    public static void main(String... args) {
        ArrayList<Runnable> closures = new ArrayList<>();

        for (int i: [1, 2]) {
            int tmp = i
            closures.add(() -> System.out.println(tmp));
        }

        for (Runnable closure: closures)
            closure.run();
    }
}
{code}

> Captured loop variables have surprising and Java-incompatible behavior
> ----------------------------------------------------------------------
>
>                 Key: GROOVY-8826
>                 URL: https://issues.apache.org/jira/browse/GROOVY-8826
>             Project: Groovy
>          Issue Type: Bug
>    Affects Versions: 3.0.0-alpha-3
>            Reporter: Роман Донченко
>            Priority: Major
>
> Consider this source:
> {code:java}
> import java.util.ArrayList;
> import java.util.Arrays;
> public class Test {
>     public static void main(String... args) {
>         ArrayList<Runnable> closures = new ArrayList<>();
>         for (int i: new int[] {1, 2})
>             closures.add(() -> System.out.println(i));
>         for (Runnable closure: closures)
>             closure.run();
>     }
> }
> {code}
> If it's compiled as Java, the output is:
> {code}
> 1
> 2
> {code}
> But if it's compiled as Groovy, the output is:
> {code}
> 2
> 2
> {code}
> In other words, in Java each iteration gets a unique instance of the {{i}} variable, which is captured in the corresponding closure, while in Groovy, only one {{i}} variable exists and is captured into both closures. IMO, the Groovy behavior is significantly less useful, and it would be nice if in 3.0 it was changed to match Java.
> Groovy also exhibits the same behavior with Groovy closures and {{for(...in...)}} loops. I just used Java-compatible syntax for this example in order to contrast Groovy and Java.



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