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From "Daniel Sun (JIRA)" <>
Subject [jira] [Commented] (GROOVY-8409) Static compilation with generic function wrapping BiFunction causes GroovyCastException
Date Sat, 18 Aug 2018 10:02:00 GMT


Daniel Sun commented on GROOVY-8409:

The content of resolvedPlaceholders is shown as follows:
{R=T, T=java.util.Date,}
Note: the `T` of `R=T` is defined by user, but the `T` of `T=java.util.Date` is defined in
`BiFunction`. We should not just use generics name whose type is `String`.


The relevant code is:

        Map<String, GenericsType> resolvedPlaceholders = resolvePlaceHoldersFromDeclaration(receiver,
getDeclaringClass(method, arguments), method, method.isStatic());
        if (!receiver.isGenericsPlaceHolder()) {
            GenericsUtils.extractPlaceholders(receiver, resolvedPlaceholders);

> Static compilation with generic function wrapping BiFunction causes GroovyCastException
> ---------------------------------------------------------------------------------------
>                 Key: GROOVY-8409
>                 URL:
>             Project: Groovy
>          Issue Type: Bug
>          Components: Static compilation
>    Affects Versions: 2.4.8, 2.4.13
>         Environment: MacOS Sierra 10.12.6
>            Reporter: Shon Vella
>            Priority: Major
>         Attachments: Bug.groovy
> I have a statically compiled with a method declares Generic type T as it's return type
and accepts a parameter of type java.util.function.BiFunction also with return type T. It
makes a call to the passed in BiFunction and assigns the the result to a variable of type
> {code:java}
> static <T> T actionWrapperT(BiFunction<Date, URL, T> action) {
>         T result = action.apply(new Date(), new URL(''))
>         // do something else here
>         return result
>     }
> {code}
> When actionWrapperT is called with runtime type of T as something other the Date, it
causes a GroovyCastException.
> {panel}
> org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'XXX@71b1176b'
with class 'XXX' to class 'java.util.Date'
> {panel}
> because it incorrectly tries to cast result type Date rather than to .
> It appears to me that the compiler is conflating generic type T as declared for the generic
method with generic type T as declared by BiFunction<T,U,R> because if I change the
name of the generic type of the generic method to R (to match the return type name of BiFunction)
or to some other name not used by BiFunction, then it works correctly, but if I change it
to U to match the second parameter of the BiFunction then it fails trying to cast to the BiFunction
generic type U instead of the method generic type U.
> Problem does not happen under normal compilation or with only type checking enabled.
> Attached file Bug.groovy reproduces the problem.

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