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Exercise: Generic Consumer

In your project, you use a class that represents a consumer of some type. You have two implementations of this class: Printer and Sender. A printer that can accept Number should also accept Int and Double. A sender that can accept Int should also accept Number and Any. In general, a consumer that can accept T should also accept S if it is a subtype of T. Update the Consumer, Printer and Sender classes to achieve this.

abstract class Consumer<T> {
    abstract fun consume(elem: T)
}

class Printer<T> : Consumer<T>() {
    override fun consume(elem: T) {
        // ...
    }
}

class Sender<T> : Consumer<T>() {
    override fun consume(elem: T) {
        // ...
    }
}

Example usage:

val p1 = Printer<Number>()
val p2: Printer<Int> = p1
val p3: Printer<Double> = p1

val s1 = Sender<Any>()
val s2: Sender<Int> = s1
val s3: Sender<String> = s1

val c1: Consumer<Number> = p1
val c2: Consumer<Int> = p1
val c3: Consumer<Double> = p1

This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in advanced/generics/Consumer.kt. You can find there starting code and example usage.

Once you are done with the exercise, you can check your solution here.

Playground

abstract class Consumer<T> {
    abstract fun consume(elem: T)
}

class Printer<T> : Consumer<T>() {
    override fun consume(elem: T) {
        // ...
    }
}

class Sender<T> : Consumer<T>() {
    override fun consume(elem: T) {
        // ...
    }
}

fun main(args: Array<String>) {
    val p1 = Printer<Number>()
    val p2: Printer<Int> = p1
    val p3: Printer<Double> = p1
    
    val s1 = Sender<Any>()
    val s2: Sender<Int> = s1
    val s3: Sender<String> = s1
    
    val c1: Consumer<Number> = p1
    val c2: Consumer<Int> = p1
    val c3: Consumer<Double> = p1
}