What is the proper way to create new instance of generic class in kotlin?

If you let IntelliJ add explicit type information, you see that entityClass is actually of type Class<Class<String>>. I’m not sure if that’s what you want. In line 2 you are first creating an instance of Class<T> and then one of T but that’s not possible anyway, because the generic information about T is lost at runtime. Apart from that you can’t instantiate class objects directly.

Solution

One possible solution would be to add a parameter of type Class<T> to your function or class and use it to instantiate objects like this.

fun <T> foo(entityClass: Class<T>) {
    var entity: T = entityClass.newInstance()
}

fun test() {
    foo(Object::class.java)
}

But there’s actually a more elegant solution without the use of reflection. Define a parameter of method type () -> T and use constructor references. Here’s my related question about constructor references and here’s the code:

fun <T> foo2(factory: () -> T) {
    var entity: T = factory()
}

fun test() {
    foo2(::Object)
}