In Kotlin, how can I get a class from a string and assign it to a variable with superclass type?

Question

Right now I am using this line: klass = Class.forName({MyClassName}).kotlin as KClass<{MySuperClassName}>

But I am getting an 'unchecked cast' warning

Is there a better way to do it?

Answer 1

I don't see a way to avoid this warning because .kotlin is an extension of <T : Any> Class<T> and that's what Class.forName() is returning (when translated from Java). So what you're actually doing looks like this:

Class.forName() -> Class<T: Any>.kotlin -> KClass<T: Any> as KClass<{MySuperClassName}>

You are casting KClass<T: Any> to KClass<{MySuperClassName}> and that will always produce a warning because the compiler can't tell if MySuperClassName is in fact a descendant of T because T can be anything at this point.

Answer 2

This cast is actually incorrect; a Class<{MyClassName}> is not a Class<{MySuperClassName}>. It only doesn't throw an exception because, as the warning says, the cast is unchecked. The type you probably want is Class<out {MySuperClassName}> (meaning basically Class<some subtype of {MySuperClassName}>).

Fixing the type won't fix the warning for reason already explained in Sir Codesalot's answer.

But you can suppress the warning with @Suppress("UNCHECKED_CAST") because no, there is no better way to do it.