[jira] [Resolved] (GROOVY-11508) Multiple traits with related generic types cannot be used

["Eric Milles (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/GROOVY-11508?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Eric Milles resolved GROOVY-11508.
----------------------------------
    Fix Version/s: 4.0.24
       Resolution: Fixed

> Multiple traits with related generic types cannot be used
> ---------------------------------------------------------
>
>                 Key: GROOVY-11508
>                 URL: https://issues.apache.org/jira/browse/GROOVY-11508
>             Project: Groovy
>          Issue Type: Bug
>          Components: Compiler
>    Affects Versions: 4.0.0
>            Reporter: James Daugherty
>            Assignee: Eric Milles
>            Priority: Major
>             Fix For: 4.0.24
>
>         Attachments: screenshot-1.png, screenshot-2.png, screenshot-3.png
>
>
> When updating Grails from Groovy 3.x to 4.x we discovered that GROOVY-5106 prevents us from updating to Groovy 4 for the [grails-data-mapping|https://github.com/grails/grails-data-mapping] (GORM) project.  Groovy-5106 does not take into account relationships between generic types and groovy does not support inheritance in generic types on traits so we have no workable solution for using Groovy 4.
>  
> For example, the following is not possible in Groovy 4:
> {code:java}
> class Parent extends GormEntity<Parent> {
> }
> class Child extends GormEntity<Child> {
> } 
> class GormEntity<? extends GormEntity> { // ? extends GormEntity is not allowed
> }{code}
>  
> We have documented the impacts of this issue on the grails-data-mapping project here:  [https://github.com/grails/grails-data-mapping/issues/1811]   We have discovered that the original change could be reverted and continue to work with the latest Java & Groovy. 
>  
> For Grails Data Mapping (GORM), there is support for inheritance between a Parent & Child domain object.  This is often implemented like this:
> {code:java}
> class Parent extends GormEntity<Parent> {
> }
> class Child extends GormEntity<Child> {
> }
> trait GormEntity<D> { // Simplified for this ticket
>     static D get(Serializable id)
>    
>     static List<D> getAll()
> }
>  {code}
> This allows someone to do the following in code:
> {code:java}
> Parent.get(1L) // Will find either a Child or Parent
> Child.get(1L) // Will find only child types{code}
>  
> Since Groovy-5106 does not take into account inheritance, can this change be reverted or changed to a warning until inheritance is taken into account?



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