// specifies that any data type
// that is "renderable" *must*
// have a "render" function that
// returns a string (possibly);
// we don't care how it gets the
// job done, nor any other data/
// functions
interface IRenderable {
    fun render(): String
}



















// given that info, we can then
// write functions that work with
// renderable types (even before
// those types are known!)

// outputs renderable types render to the screen
fun speak(communicative: List<IRenderable>) {
    communicative.forEach {
        println(it.render())
    }
}




























// examples that "implement" this interface
// by "overriding" the required render function

data class Puppy(val name: String): IRenderable {
    // puppies always say the same thing :P
    override fun render(): String = "Woof!"
}

data class Emoji(val symbol: String): IRenderable {
    // emoji differ a bit
    override fun render(): String = symbol
}

speak(listOf(
    Puppy("Toto"),
    Puppy("Scooby"),
    Puppy("Lassie"),
    Emoji("👋"),
    Emoji("🤓"),
))