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

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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)
}

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