How do I create an Array<T> (like Array<S...

# reflect

[maxmello]

How do I create an Array<T> (like Array<String>, Array<MyClass> etc.) from a List<T>, with the Array actually being the type T, not Array<Any?>? I’m inside an inline function with reified type parameter, so I should know the T KClass, but how do I dynamically create an Array<T>? I tried calling the Array constructor public inline constructor(size: Int, init: (Int) -> T) via reflection, but I don’t know how that second parameter is supposed to work.

[ephemient]

generally can't call inline functions with reified type parameters via reflection, and Array is even more special, being handled specifically by the compiler

[ephemient]

I think your only choice may be to use

java.lang.reflect.Array.newInstance(T::class.java, size) as Array<T>

if you can't use Array<T>(size) {...} directly

[maxmello]

I will try that tomorrow, thank you

[ilya.gorbunov]

How do I create an Array<T> from a List<T>?

if the type T is known at compile time, you can just use list.toTypedArray()

[ephemient]

if you have reified T then that works, but so would the Array() "constructor" so I assumed Max didn't have that available for some reason

[maxmello]

The approach with java reflect worked 🙂
I only “know” T as this is a inline function with reified type parameter, I iterate through its props and do this:

if(prop.returnClass.java.isArray) {
   val foundGenericType = prop.returnType.arguments.firstOrNull()?.type
   val genericClass = foundGenericType?.classifier as? KClass<*>
   val listVal = (prop as? KProperty1<T, Array<*>?>)?.get(this)?.toList()
   val outputList = // Operate on list instead of array to generate output for reasons
   val array = java.lang.reflect.Array.newInstance(genericClass?.java, outputList.size) as Array<Any?>
     outputList.forEachIndexed { index, any ->
        array[index] = any
     }
  return array
}

So I have a KClass, I would love to be able to do list.toTypedArray<genericClass::asTypeParameter>() 😄