Functional Kotlin

Invoke

Back in Chapter 2, Getting Started with Functional Programming, in the section First-class and high-order functions, when we introduced lambda functions, we show the definition of Function1:

/** A function that takes 1 argument. */public interface Function1<in P1, out R> : Function<R> {    /** Invokes the function with the specified argument. */    public operator fun invoke(p1: P1): R}

The invoke function is an operator, a curious one. The invoke operator can be called without name.

The class Wolf has an invoke operator:

enum class WolfActions {   SLEEP, WALK, BITE}class Wolf(val name:String) {   operator fun invoke(action: WolfActions) = when (action) {      WolfActions.SLEEP -> "$name is sleeping"      WolfActions.WALK -> "$name is walking"      WolfActions. ...