Functions as values

We already covered some of the functional capabilities of Kotlin in the chapters dedicated to Design Patterns. The Strategy and Command design patterns are but a few that heavily rely on the ability to accept functions as arguments, return functions, store them as values, or put them inside collections. In this section, we'll cover some other aspects of functional programming in Kotlin, such as function purity and currying.

Higher-order functions

As we discussed previously, in Kotlin, it's possible for a function to return another function:

fun generateMultiply(): (Int, Int) -> Int {
return { x: Int, y: Int -> x * y}
}

Functions can also be assigned to a variable or value to be invoked later on:

val multiplyFunction = generateMultiply()
...
println(multiplyFunction(3, 4))

The function assigned to a variable is usually called a literal function. It's also possible to specify a function as a parameter:

fun mathInvoker(x: Int, y: Int, mathFunction: (Int, Int) -> Int) ...