@north don’t really know if it’s ok, but this works:

interface TestInterface {
    fun apply(str: String): String
}

fun TestInterface(lambda: (String) -> String): TestInterface {
    return object : TestInterface {
        override fun apply(str: String): String = lambda(str)
    }
}

fun main(args: Array<String>) {
    var test = TestInterface { str: String -> str.apply { println(str) } }
    test.apply("test")
}

You can throw some inlines in there.

kojdecki: thank you. this was a solution I also found in one of the linked threads. To be fair, I think this language limitations should be lifted. Adding boiler plate code to our interfaces is a workaround.