Is there a reliable way to determine the class of ...

# getting-started

[Landry Norris]

Is there a reliable way to determine the class of a reified generic, including typedefs? I tried a when(T::class), but I can’t use X::class when X is a typedef. I would like to distinguish X and Y, where X and Y are both typedefs for class Z.

[Landry Norris]

The reason is that I’m writing a helper method for JNI methods. I need the signature of a method, so I am using reified generics in an inline method for this. I can check T::class against Int::class, Double::class, etc to get the proper signature. I can’t check against jstring/jobject, however, since both are typedefs for CPointers.

[ephemient]

the problem with KClass is generic erasure, not typedef. try KType,

typeOf<X>()

[Landry Norris]

I’ll take a look at that.

[Landry Norris]

Is there a performance hit due to reflection? I should mention this is K/N, so I don’t know as much about reflection on K/N.

[ephemient]

on JVM it does result in some kotlin-reflect machinery being loaded, but I don't know about K/N

[Landry Norris]

I’ll have to try this out tonight and see if it helps.

[Landry Norris]

I tried using a when with typeOf, but when I pass in a typeOf a typedef, it always triggers the when branch with the first type that has the same underlying class. If I have

when(type) {
    typeOf<jstring> -> "String"
    typeOf<jobject> -> "Object"
}

and pass in typeOf<jobject>, it returns “String”

[Landry Norris]

where jstring and jobject are both typedefs for CPointer

[ephemient]

oh, I see. there is typedef jobject jstring in jni.h. so they are 100% indistinguishable in C and in Kotlin.

[Landry Norris]

Yeah. I'm trying to write a method that uses reified generics to automatically get the signature of a method. I have it working for everything except typedefs. The Kotlin signature is known at compile time, I just want to create a string using it.

[ephemient]

typedef doesn't really exist, you can think of every usage as being immediately substituted before compilation

[Landry Norris]

Yeah. I may need to make some sort of compiler plugin