Hands-On Design Patterns with Kotlin

Find family

Say you have an unordered list of objects:

data class Person(val firstName: String,                   val lastName: String,                  val age: Int)val people = listOf(Person("Jane", "Doe", 19),            Person("John", "Doe", 24),            Person("John", "Smith", 23))

And would like to find a first object that matches some criteria. Using extension functions, you could write something like this:

fun <T> List<T>.find(check: (T) -> Boolean): T? {    for (p in this) {        if (check(p)) {            return p        }    }    return null}

And then, when you have a list of objects, you can simply call find() on it:

println(people.find {    it.firstName == "John"}) // Person(firstName=John, lastName=Doe)

Luckily, you don't have to implement anything. This method is already implemented for you in Kotlin.

There's ...