What if I have a `MapBuilder lt String String gt ` kotlinlang #getting-started

karelpeeters

11/16/2018, 6:17 PM

What if I have a

MapBuilder<String, String>

11/16/2018, 6:21 PM

karelpeeters

11/16/2018, 6:23 PM

... and I call

invoke("hello")

on it. Which one should it call?

11/16/2018, 6:29 PM

How can I solve it without set bound to one of types?

I was thinking early, that T and U must be the different types

11/16/2018, 6:34 PM

Any ideas how can I realize this?

obviously you cannot

karelpeeters

11/16/2018, 7:36 PM

Well either they must be different types in which case you just set bounds or they can be the same type and your approach can fundamentally not work.

11/18/2018, 5:30 PM

You may do run time type checking:

inline fun <reified T, reified U> mapBuilder() = MapBuilder(T::class.java, U::class.java)

class MapBuilder<T, U>(
        private val tClass: Class<T>,
        private val uClass: Class<U>
) {
    operator fun invoke(arg: Any): MapBuilder<T, U> {
        when {
            tClass.isAssignableFrom(arg.javaClass) -> {
                // you got a T
            }
            uClass.isAssignableFrom(arg.javaClass) -> {
                // you got a U
            }
            else -> // you got an invalid argument
                throw IllegalArgumentException("Arg ${arg.javaClass} is not a $tClass or $uClass")
        }
        return this
    }
}

mapBuilder<String, Int>()("Hello")(1234)("World!")

Though I would not do this, whatever you are trying to do I am sure there is a better way that still gives you a clean syntax for your builder.