Kotlin interfaces and operator overloading

interfacesSample.kt

interface Donkey {
    fun speak(speech: String)
}

fun interface ISpeechDevice {
    operator fun invoke(speech: String)
}

class PrintDevice: ISpeechDevice {
    override fun invoke(speech: String) {
        println(speech)
    }
}

class TextFileDevice: ISpeechDevice {
    override fun invoke(speech: String) {
        println("Writing '$speech' to some file...")
    }
}

class RealDonkey(private val device: ISpeechDevice) : Donkey {
    override fun speak(speech: String) {
        device(speech)
    }
}

class Person(
    val name: String,
    val age: Int
) {
    
    operator fun plus(p2: Person): Person {
        return Person(
            name = name + p2.name,
            age = age + p2.age
        )
    }

    operator fun plus(i: Int): Person {
        return Person(
            name = name,
            age = age + i
        )
    }

    fun intro() {
        println("Hi I'm $name and I'm $age years old.")
    }
}

fun people() {
    val p1 = Person("Jake", 20)
    val p2 = Person("Simon", 30)

    p1.intro() // Jake 20
    p2.intro() // Simon 30
    (p1 + 10).intro() // Jake 30
    (p1 + p2).intro() // JakeSimon 50
}

fun speakingDevices() {
    val pDevice = PrintDevice()
    val tDevice = TextFileDevice()
    val d1 = RealDonkey(pDevice)
    val d2 = RealDonkey(tDevice)
    val d3 = RealDonkey{
        println("THe magic device says: $it")
    }
}

fun main() {

}