Hands-On Design Patterns with Kotlin

Filter family

Another common task is filtering a collection. You know the drill. You iterate over it and put only values that fit your criteria in a new collection. For example, if given a range of numbers between 1-10, we would like to return only odd ones. Of course, we've already learned this lesson from the previous example, and wouldn't simply create a function called filterOdd(), as later we would be required to also implement filterEven(), filterPrime(), and so on. We'll receive a lambda as the second argument right away:

fun filter(numbers: List<Int>, check: (Int)->Boolean): MutableList<Int> {    val result = mutableListOf<Int>()    for (n in numbers) {        if (check(n)) {            result.add(n)        }    }    return result}

Invoking it will print only odd numbers. ...