Kotlin function argument without type annotation

Question

On Kotlin, Arguments of a function require their type annotation when defining the method.

In my case, I have two classes from an interface.

interface Base{
    fun method()
}

class DervA():Base{
    fun override method(){
        ...
    }
}

class DervB():Base{
    fun override method(){
        ...
    }
}

And, I hope to call their methods from other function like

fun test_method(inst){
    inst.method()
}

But, Kotlin compiler complains "a type annotation is required on a value parameter" .

Should I define "test_method" for each of the classes ?

fun test_method_for_DervA(inst:DervA){
    inst.method()
}

fun test_method_for_DervB(inst:DervB){
    inst.method()
}

Do you have any smarter way for it?

Answer 1

You can just do

fun testMethod(inst: Base) {
    inst.method()
}

Since both DervA and DervB are Bases, they can also be passed to testMethod and their overridden method will be called. That's one of the fundamental principles of OOP.

---

Note that if method and testMethod have the same return type, you can shorten it to

fun testMethod(inst: Base) = inst.method()