Constrained genericity: Difference between revisions

=={{header|Kotlin}}==

In the following program we define an interface, Eatable, and two classes - Cheese and Meat - which implement it and must therefore implement its eat() method because the interface itself does not provide a default implementation.

We then define a generic class, FoodBox, whose type parameter, T, is constrained to an Eatable type and instantiate it using both the Cheese and Meat types:

<lang scala>// version 1.0.6

interface Eatable {

fun eat()

}

class Cheese(val name: String) : Eatable {

override fun eat() {

println("Eating $name")

}

override fun toString() = name

}

class Meat(val name: String) : Eatable {

override fun eat() {

println("Eating $name")

}

override fun toString() = name

}

class FoodBox<T: Eatable> {

private val foodList = mutableListOf<T>()

fun add(food: T) {

foodList.add(food)

}

override fun toString() = foodList.toString()

}

fun main(args: Array<String>) {

val cheddar = Cheese("cheddar")

val feta = Cheese("feta")

val cheeseBox = FoodBox<Cheese>()

cheeseBox.add(cheddar)

cheeseBox.add(feta)

println("CheeseBox contains : $cheeseBox")

val beef = Meat("beef")

val ham = Meat("ham")

val meatBox = FoodBox<Meat>()

meatBox.add(beef)

meatBox.add(ham)

println("MeatBox contains : $meatBox")

cheddar.eat()

beef.eat()

println("Full now!")

}</lang>

{{out}}

<pre>

CheeseBox contains : [cheddar, feta]

MeatBox contains : [beef, ham]

Eating cheddar

Eating beef

Full now!

</pre>