[GROOVY-2829] Groovy's class verification doesn't allow for covariant return types

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.6-beta-1
• Fix Version/s: 1.5.7, 1.6-beta-2
• Assignee: Jochen Theodorou
• Reporter: Paul King
• Created: 16/May/08 04:52
• Updated: 07/Apr/15 19:07
• Resolved: 29/May/08 00:20

Description

Given these Java interfaces:

import java.util.List;

public interface Base {
    List foo();
}

import java.util.ArrayList;

public interface Child extends Base {
    ArrayList foo();
}

Java allows the return type for methods to be the most specified or a derived type:

import java.util.ArrayList;

public class JavaChildImpl implements Child {
    public ArrayList foo() {
        return null;
    }
}

But compiling this Groovy script:

class GroovyChildImpl implements Child {
    public ArrayList foo() {
        return null
    }
}

yields:

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed, GroovyChildImpl.groovy: 2: the return type is incompatible with java.util.List foo() in Base.
Node: org.codehaus.groovy.ast.MethodNode. At [2:5]  @ line 2, column 5.
       public ArrayList foo() {
       ^

1 error

Attached patch fixes this problem.