Hands-On Design Patterns with Kotlin

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) {    println(mathFunction(x, y))}mathInvoker(5, 6, multiplyFunction)

If a function is the last parameter, it can also be supplied ad hoc, outside of the brackets:

mathInvoker(7, 8) { x, y ->   x * y}

In general, ...