Anyone saw this error when trying to run property based test kotlinlang #kotest

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Title

Kiryushin Andrey

04/27/2020, 2:57 PM

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

04/27/2020, 3:01 PM

Can you post up code that causes that ?

Kiryushin Andrey

04/27/2020, 3:02 PM

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

sam

04/27/2020, 3:03 PM

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

Kiryushin Andrey

04/27/2020, 3:03 PM

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

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

04/27/2020, 3:03 PM

right

we can fix the exception

Kiryushin Andrey

04/27/2020, 3:04 PM

it's a bit obscure, yes

sam

04/27/2020, 3:04 PM

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

04/27/2020, 3:05 PM

yep, thanks for help! I will try to

sam

04/27/2020, 3:05 PM

so something like

forAll(Graph.strings()) { graph -> }

the

forAll<A, B, ... N>

syntax is shorthand for that

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

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