how do I call the constructor of a generic type? Say I have something like

class foo<T: Interface>() {
    var something: T? = null
    init {
        something = T("bar") //doesn't work
    }
}

I have an interface, the implementing classes of which have a constructor that takes one string. I'd like to make a class that can take any type that implements the interface and be able to cosntruct an instance of said class.

You can't, because you cannot guarantee that every

T

that implements

Interface

will have a constructor that takes a single string argument.

I have a machine translation program that can implement several translation APIs like google translate and deepl. These are implemented as children of a common interface. I'd like to also add tornadoFX fragments that can set the api key of each of these classes through a settings dialog. Right now I have a separate form for each but this duplicates code when really the only unique part of the settings form is the type of translation backend class it uses

Same problem. Just that the abstract class has that constructor does not mean a subclass has such a constructor.

so the generics can't really be used with polymorphism then?

You can pass a function to the

Foo

class

yeah just found on stack overflow to pass a (String) -> T to it

You can also store the function itself as a property of the class, if you need to use it multiple times, or call it later instead of immediately at construction time:

class Foo<T>(private val createThing: (String) -> T) {
    fun doStuff() {
        val thing = createThing()
        // ...
    }
}