Is it possible to modify the Kotlin compiler to support `reified` type parameters in non-inlined fun...

# multiplatform

[Giorgio Spilorcio]

Is it possible to modify the Kotlin compiler to support reified type parameters in non-inlined functions by passing the Class<T> as an additional parameter at runtime? For example:

fun <reified T : A> doStuff(s: String): T {
    Debug.log(T::class.java)
}

would compile in the JVM to:

public static final <T extends A> void doStuff(Class<T> reifiedType, String s) {
    Debug.log(reifiedType);
}

Can this feature be added to Kotlin or would it require big changes?

[ephemient]

no, there are things reified T can do that Class<T> cannot

[chrisjenx]

Also Class is a java construct. So that wouldn't work on multiplatform anyway. It's best to use KType.

Generally if you need more information at runtime but don't want to manually pass it through, that's where compiler plugins will generate extra code. Think descriptors for kotlinx serialization

[Giorgio Spilorcio]

I tought it was possible since extension functions did something similar

[Giorgio Spilorcio]

no, there are things reified T can do that Class<T> cannot

Can you tell me an example please?

[ephemient]

well one is that Class is a Java concept so

val a: Class<out Any> = List::class.java
val b: Class<out Any> = MutableList::class.java
a == b

[ephemient]

but also even KClass has limitations, such as having generics erased, while reified T isn't

[ephemient]

also <T> can be nullable or non-nullable, and `Class`/`KClass` are always non-nullable, and if you define

inline fun <reified T> emptyArray(): Array<T> = Array(0) { TODO() }

then it's safe to call emptyArray<String>() and emptyArray<Int>(), but if you define

fun <T> emptyArray(clazz: Class<T>): Array<T> = java.lang.reflect.Array.newInstance(clazz, 0) as Array<T>

then while emptyArray(String::class.java) works, emptyArray(Int::class.java) will throw a ClassCastException because primitives in Java are deeply special