Kotlin — Generics

Generic class

class Box<T>(val value: T)

val intBox = Box(42)
val strBox = Box("Hello")

Generic function

fun <T> singletonList(item: T): List<T> {
    return listOf(item)
}

fun <T> List<T>.second(): T {
    return this[1]
}

Type constraints

fun <T : Comparable<T>> sort(list: List<T>): List<T> {
    return list.sorted()
}

fun <T> printWhenNotEmpty(item: T) where T : CharSequence, T : Comparable<T> {
    if (item.isNotEmpty()) println(item)
}

Star projection

fun printList(list: List<*>) {
    list.forEach { println(it) }
}

Mini Practice

Write Kotlin code that:

1. Creates a generic class
2. Writes a generic function
3. Uses type constraints
4. Demonstrates star projection

Up Next

In the next lesson, you'll learn about DSL — domain-specific languages.