How to check whether the type of objects inside a ...

# reflect

[albertgao]

How to check whether the type of objects inside a List<*> is a kotlin official class or my own class, I currently check its name: paramName.substring(24).removeSuffix(">"), so "kotlin.collections.List<nz.salect.objJSON.Lesson>" will become "nz.salect.objJSON.Lesson", and then I can verify whether it startsFrom("kotlin") or not. What’s a better way to do this?

[udalov]

KType.arguments

[albertgao]

@udalov Thanks! I solved this via this param.type.arguments[0].type?.classifier as KClass<*>

[udalov]

Beware of the fact that type's classifier may not be a class, e.g.

fun <T> foo(): List<T>

here List<T> is a list of T, which is not a KClass and therefore will crash with ClassCastException

[albertgao]

@udalov Thanks for the reply, do you mean that I should try catch this as cast to handle the potential ClassCastException?

[udalov]

No. It's never a good idea to catch ClassCastException. What I'm saying is that if this situation (type variables) is possible in your use case, you should handle it by inspecting the type of the returned classifier. KType.classifier returns KClassifier, which has exactly two subclasses: KClass and KTypeParameter. So if this is possible in your use case, you should have code like

val type = param.type.arguments.first().type
when (type.classifier) {
    is KClass<*> -> ...
    is KTypeParameter -> ...
    else -> throw UnsupportedOperationException()
}

Or, a completely different approach, which I suggested in another thread, is to use jvmErasure which always gives the KClass but loses type information about generics which might be valuable in your use case (again, I don't know what you're using this for, but it might be better one way or the other)