Why kotlin script file cannot have inherited class in the same file?

Question

I'm wring my.kts script, and use it to run kotlin, I've got this:

class TestA {
    init {}
    open fun testOpen() {
        println(this)
    }
}
class TestB : TestA {
    override fun testOpen() {
        super.testOpen()
    }
}

It fails to compile, saying that:

error: this type is final, so it cannot be inherited from
class TestB : TestA {
          ^
basic.kts:39:15: error: this type has a constructor, and thus must be     initialized here

class TestB : TestA {

Answer 1

If you inherit one class from another and base class has primary constructor, it must be initialised. Your TestA has default primary constructor, so it should look like:

class TestB : TestA() {
    override fun testOpen() {
        super.testOpen()
    }
}

Another problem is that classes in kotlin are final by default and you should explicitly define that they can be extended:

open class TestA

Check this examples for more information.