Facing a weird case here, I have the following function:

fun <T> test(param: T) {
    val clazz = param::class
}

And the compiler complains (rightly so) that param has a nullable type 'T'. It even suggests using

!!

to make it non-nullable, but if I do that, the compiler still complains with the exact same message. Here are a few more variations I've tried, each one with the same error message:

val clazz = param!!::class
val clazz = param?.let { it::class }
val clazz = if (param != null) param::class else null

So, how am I supposed to get to the class of

param

here? Is this a bug with type inference or am I missing something? Making

T

reified or constrain it to

Any

is not an option.

why can’t you constrain it to Any?

Because the function I'm actually doing this in is overriding a function from an interface I have no control over.

I definitely think this is a bug: extensions functions do in fact work fine:

fun Any.foo() = print(this.toString())

fun <T> bar(param: T) {
    if (param != null) {
        println(param.foo())
        println(param::class)
    }
}

Yes, will do!

Looks like someone got there before you did: https://youtrack.jetbrains.net/issue/KT-20778

Ah right, thank you! And it's already 11 months old...

(x as Any?)?.let { it::class }

works too and doesn't do the useless

INSTANCEOF java/lang/Object

check at runtime 😒imple_smile:

Yeah that's better, didn't even think about that 😄

Um, I have no clue what

param!!::class

does. Aren't you looking for

param.javaClass

? Just requires it to be non-null. Well, just add a constraint

<T : Any>

As discussed that's not an option, and this is definitely a bug.

Yup, not an option, although I think

param?.javaClass

might work in my case, but won't work if you actually need the KClass.

Yeah, I agree that what I just tested is behaving unlike what I would expect.

param!!::class

is just asserting

param

to be non-null, and then getting it's

KClass

. At least that's what it should do.

Oh right, ::class can give you the

KClass

of the object

It is, see my code 😛. It just doesn't work for

::class

for some reason.

Alright, I guess

::class

is a special case then.

Must be, I'm looking around in the source.