Anyone saw this error when trying to run property-based test using generic types? ```java.lang.Class...

# kotest

[Kiryushin Andrey]

Anyone saw this error when trying to run property-based test using generic types?

java.lang.ClassCastException: java.base/sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl cannot be cast to java.base/java.lang.Class

[sam]

Can you post up code that causes that ?

[Kiryushin Andrey]

forAll<Graph<String>> { graph ->
    graph.isNotEmpty()
}

[sam]

Ok, seems like it doesn't like higher kinded types

[Kiryushin Andrey]

I guess the error has to do with the fact that execution ends up in an inline function with a reified type parameter, yes...

[Kiryushin Andrey]

The type parameter of Graph type constructor gets erased, so the the runtime has no means to figure out how to instantiate instances of requested type

[sam]

right

[sam]

we can fix the exception

[Kiryushin Andrey]

it's a bit obscure, yes

[sam]

but it won't work anyway, as the Graph type isn't built in, so it has no way of knowing which arb to use. You would need to pass in the gen.

[Kiryushin Andrey]

yep, thanks for help! I will try to

[sam]

so something like forAll(Graph.strings()) { graph -> }

[sam]

the forAll<A, B, ... N> syntax is shorthand for that

[sam]

https://github.com/kotest/kotest/issues/1416