Variance: in और out

open class Animal(val name: String)
// Define a class `Dog`
class Dog(name: String) : Animal(name)

// Define a class `Box`
class Box<T>(val item: T)

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `dogBox` (a `Box<Dog>`), set to `Box(Dog("Rex"))`
    val dogBox: Box<Dog> = Box(Dog("Rex"))
    // Print `dogBox.item.name` to the console, with a trailing newline
    println(dogBox.item.name)
}

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open class Animal(val name: String)
// Define a class `Dog`
class Dog(name: String) : Animal(name)

// Define a class `Producer`
class Producer<out T>(private val item: T) {
    // Define the function `produce` with no parameters and returning a `T`
    fun produce(): T = item
}

// Define the function `printAnimalName` taking `producer`
fun printAnimalName(producer: Producer<Animal>) {
    // Print `producer.produce().name` to the console, with a trailing newline
    println(producer.produce().name)
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `dogProducer` (a `Producer<Dog>`), set to `Producer(Dog("Rex"))`
    val dogProducer: Producer<Dog> = Producer(Dog("Rex"))
    printAnimalName(dogProducer)
}

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open class Animal(val name: String)
// Define a class `Dog`
class Dog(name: String) : Animal(name)

// Define a class `Consumer`
class Consumer<in T> {
    // Define the function `consume` taking `item`
    fun consume(item: T) {
        // Print "Consuming an item" to the console, with a trailing newline
        println("Consuming an item")
    }
}

// Define the function `feedDog` taking `consumer`
fun feedDog(consumer: Consumer<Dog>) {
    consumer.consume(Dog("Rex"))
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `animalConsumer` (a `Consumer<Animal>`), set to `Consumer()`
    val animalConsumer: Consumer<Animal> = Consumer()
    feedDog(animalConsumer)
}

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open class Animal(val name: String)
// Define a class `Dog`
class Dog(name: String) : Animal(name)

// Define the function `printNames` taking `animals`
fun printNames(animals: List<Animal>) {
    // Loop over `animals) println(animal.name`, binding each item to `animal`
    for (animal in animals) println(animal.name)
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `dogs` (a `List<Dog>`), set to `listOf(Dog("Rex"), Dog("Fido"))`
    val dogs: List<Dog> = listOf(Dog("Rex"), Dog("Fido"))
    printNames(dogs)
}

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