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https://issues.apache.org/jira/browse/GROOVY-9762?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Marcin Zajaczkowski updated GROOVY-9762:
----------------------------------------
    Description: 
I've encountered a problem with type checking if a method reference is used.

In following (stripped down from the original production case) code in the line 
with the error variable the following error is reported:
{code:java}
> Task :compileTestGroovy
startup failed:
/home/foobar.../MethodReferenceProblemWithType.groovy: 15: [Static type 
checking] - Cannot assign value of type java.lang.Object to variable of type 
java.util.List <Integer>
 @ line 15, column 31.
 List<Integer> error = opt.map(this::just).get()  {code}
{code:java}
@CompileStatic
class MethodReferenceProblemWithType {

    static void reproduce() {
        Optional<Integer> opt = Optional.ofNullable(Integer.valueOf(1))
        List<Integer> ok = opt.map(o -> just(o)).get()    //ok
        List<Integer> error = opt.map(this::just).get()   //problem
    }
    private static <T> List<T> just(T data) {
        return new ArrayList<T>();
    }
}  {code}
If `@CompileStatic` is removed, I still see a type incompatibility warning in 
Idea. Switching to lambda is a workaround, therefore it's just a minor glitch. 
Tested with Groovy 3.0.5.

  was:
I've encountered a problem with type checking if a method reference is used.

In following (stripped down from the original production case) code in the line 
with the error variable the following error is reported:
{code:java}
> Task :compileTestGroovy
startup failed:
/home/foobar.../MethodReferenceProblemWithType.groovy: 15: [Static type 
checking] - Cannot assign value of type java.lang.Object to variable of type 
java.util.List <Integer>
 @ line 15, column 31.
 List<Integer> error = opt.map(this::just).get()  {code}
{code:java}
@CompileStatic
class MethodReferenceProblemWithType {

    static void reproduce() {
        Optional<Integer> opt = Optional.ofNullable(Integer.valueOf(1))
        List<Integer> ok = opt.map(o -> just(o)).get()    //ok
        List<Integer> error = opt.map(this::just).get()   //problem
    }
    private static <T> List<T> just(T data) {
        return new ArrayList<T>();
    }
}  {code}

If `@CompileStatic` is removed, I still see a type incompatibility warning in 
Idea. Switching to lambda is an workaround. Tested with Groovy 3.0.5.


> Wrong type resolved if method reference used with typed method
> --------------------------------------------------------------
>
>                 Key: GROOVY-9762
>                 URL: https://issues.apache.org/jira/browse/GROOVY-9762
>             Project: Groovy
>          Issue Type: Bug
>          Components: Compiler
>    Affects Versions: 3.0.5
>            Reporter: Marcin Zajaczkowski
>            Priority: Minor
>
> I've encountered a problem with type checking if a method reference is used.
> In following (stripped down from the original production case) code in the 
> line with the error variable the following error is reported:
> {code:java}
> > Task :compileTestGroovy
> startup failed:
> /home/foobar.../MethodReferenceProblemWithType.groovy: 15: [Static type 
> checking] - Cannot assign value of type java.lang.Object to variable of type 
> java.util.List <Integer>
>  @ line 15, column 31.
>  List<Integer> error = opt.map(this::just).get()  {code}
> {code:java}
> @CompileStatic
> class MethodReferenceProblemWithType {
>     static void reproduce() {
>         Optional<Integer> opt = Optional.ofNullable(Integer.valueOf(1))
>         List<Integer> ok = opt.map(o -> just(o)).get()    //ok
>         List<Integer> error = opt.map(this::just).get()   //problem
>     }
>     private static <T> List<T> just(T data) {
>         return new ArrayList<T>();
>     }
> }  {code}
> If `@CompileStatic` is removed, I still see a type incompatibility warning in 
> Idea. Switching to lambda is a workaround, therefore it's just a minor 
> glitch. Tested with Groovy 3.0.5.



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