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

[JIRA]

Роман Донченко created GROOVY-8826:
--------------------------------------

             Summary: 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


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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