Interface Delegation unexpected results

Question

I'm trying to do a little variation of the Interface delegation example come in the official Kotlin bootcamp in => developer.android.com but I'm getting unexpected results. Please can anybody provide some hint on what's happening?:

interface IFishAction {
    fun swim();
}

interface IFishColour {
    val color: String;
}

interface IFeeding{
    fun eat( );
}

object carnivorous: IFeeding{
    override fun eat() {
        println("Meat!")
    }
}

class Shark( carnivorous: IFeeding ): IFishAction, IFishColour, IFeeding by carnivorous {
    override val color = "gray"
    override fun swim() {
        println("swim quickly")
    }
}


fun main) {
    val shark = Shark( carnivorous )
    println("---------------------------");
    println("Shark color: ${shark.color}");
    println("Shark swim: ${shark.swim()}");
}

=>
---------------------------
Shark color: gray
swim quickly
Shark swim: kotlin.Unit