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

[Daniel Sun (JIRA)]

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

Daniel Sun commented on GROOVY-8826:
------------------------------------

 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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