class MyClass(val doThis: () -> Unit, val doThat: (number: Int)  -> Unit = {}) {

    fun someFunction(){
        doThis()
        doThat(12)
    }
}

class UserClass {
    val myClass = MyClass(::doThis, ::doThat)

    private fun doThis() {

    }

    private fun doThat(number: Int) {

    }
}