How to convert a function to listOf without lamdas? - kotlin

Question

There example of works code:
package cryptography
typealias taskFun = () -> Unit
var i: Int = 0
object tasks {
val supportTaskTextList = listOf("hide", "show", "exit")
val supportTaskFunList = listOf<taskFun>(fun() { println("hide $i");i++ }, fun() { println("show $i"); i++ } , fun() { println("Bye $i"); i++ })
fun hide() {
println("Hiding message in image.")
}
fun show() {
println("Obtaining message from image.")
}
fun exit() {
println("Bye!")
kotlin.system.exitProcess(0)
}
fun getTask() {
println("Task (${supportTaskTextList.joinToString(", ")}):")
val i = readln()
for (idx in supportTaskFunList.indices)
{
if (supportTaskTextList[idx] == i) return supportTaskFunList[idx]()
}
println("Wrong task: $i")
}
}
fun main() {
while(true) {
tasks.getTask()
}
}
Is code is works. But i want to call my methods without lamda. When i tried to just use them by name i got "main.kt:4:43: error: function invocation 'hide()' expected"
in: val supportTaskFunList = listOf<taskFun> = listOf(hide, show, exit)
Yet, i can to use it like:
package cryptography
typealias taskFun = () -> Unit
// var i: Int = 0
object tasks {
val hide = fun() {
println("Hiding message in image.")
}
val show = fun() {
println("Obtaining message from image.")
}
val exit = fun() {
println("Bye!")
kotlin.system.exitProcess(0)
}
val supportTaskTextList = listOf("hide", "show", "exit")
val supportTaskFunList = listOf<taskFun>(hide, show, exit)
fun getTask() {
println("Task (${supportTaskTextList.joinToString(", ")}):")
val i = readln()
for (idx in supportTaskFunList.indices)
{
if (supportTaskTextList[idx] == i) return supportTaskFunList[idx]()
}
println("Wrong task: $i")
}
}
fun main() {
while(true) {
tasks.getTask()
}
}
May i use it without lamdas? Just, like as in C++ though pointers on methods? And why i can't use functions without lamdas here?

Answer 1

The correct syntax to reference a function by name is not using a plain name, but the :: syntax, for which you still need the name of hte object task I think. You could try just writing ::hide, ::show... but I am not sure it resolves here.,
val supportTaskFunList = listOf(tasks::hide, tasks::show, tasks::exit)
Short mention: This is a function type. According to the documentation this is not a lambda (in Kotlin terminology) as it does not define a new function or use the lambda syntax, just references an existing function.