Functional Kotlin

Inline restrictions

Inline lambda functions have an important restriction—they can't be manipulated in any way (stored, copied, and others).

The UserService stores a list of listeners (User) -> Unit:

data class User(val name: String)class UserService {   val listeners = mutableListOf<(User) -> Unit>()   val users = mutableListOf<User>()    fun addListener(listener: (User) -> Unit) {      listeners += listener   }}

  Changing addListener into an inline function will produce a compilation error:

inline fun addListener(listener: (User) -> Unit) {   listeners += listener //compilation error: Illegal use of inline-parameter listener}

If you think about it, it makes sense. When we inline a lambda, we're replacing it for its body, and that isn't something that ...