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https://issues.apache.org/jira/browse/GROOVY-7495?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Pascal Schumacher updated GROOVY-7495:
--------------------------------------
Fix Version/s: (was: 2.5.0-beta-1)
> Diamond inheritance of interfaces makes method return type incompatible
> -----------------------------------------------------------------------
>
> Key: GROOVY-7495
> URL: https://issues.apache.org/jira/browse/GROOVY-7495
> Project: Groovy
> Issue Type: Bug
> Components: Compiler
> Affects Versions: 2.3.10, 2.4.3
> Reporter: Lóránt Pintér
> Assignee: Jochen Theodorou
> Fix For: 2.4.4
>
>
> While working on Gradle, I bumped into a failure with the Groovy compiler
> that works fine in Java.
> Example code that fails with both Groovy compiler 2.3.10 and 2.4.3:
> {code:title=Groovy}
> interface Item {}
> interface DerivedItem extends Item {}
> interface Base {
> Item getItem()
> }
> class BaseImpl implements Base {
> Item getItem() { null }
> }
> interface First extends Base {
> DerivedItem getItem()
> }
> class FirstImpl extends BaseImpl implements First {
> DerivedItem getItem() { null }
> }
> interface Second extends First {}
> class SecondImpl extends FirstImpl implements Second {}
> {code}
> The error message is:
> {code}
> Script1.groovy: 8: The return type of Item getItem() in BaseImpl is
> incompatible with DerivedItem in First. At [8:3] @ line 8, column 3.
> Item getItem() { null }
> ^
> {code}
> However, changing the implementation of {{SecondImpl}} like this fixes the
> compile error:
> {code:title=Fixed Groovy}
> class SecondImpl extends FirstImpl implements Second {
> DerivedItem getItem() { super.item }
> }
> {code}
> The equivalent code compiles fine in Java:
> {code:title=Java}
> public class CompileJava {
> interface Item {}
> interface DerivedItem extends Item {}
>
> interface Base {
> Item getItem();
> }
> class BaseImpl implements Base {
> public Item getItem() { return null; }
> }
>
> interface First extends Base {
> DerivedItem getItem();
> }
>
> class FirstImpl extends BaseImpl implements First {
> public DerivedItem getItem() { return null; }
> }
>
> interface Second extends First {}
> class SecondImpl extends FirstImpl implements Second {}
> }
> {code}
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