what does this

handler: (key: K) -> V?)

means In the following function

fun getOrPut(key: String, handler: (key: String) -> V?)

i thinks

handler

is something likes the arguments name, so what are the rest? is it a lambda ?

handler

is a parameter with a function type. You could pass a lambda here, for example. https://kotlinlang.org/docs/reference/lambdas.html

Simply put, function

getOrPut(...)

receives variable named

key

of type

String

, which will be used as argument (or variable which will be used for calculating the argument ) of function

handler(...)

when invoking.

@Drasko Saric thanks So, how to set the parameter when I call

getOrPut()

function. may be like this ?

getOrPut("first arg", sampleFun("first arg"))

No. Let me explain.

if

sampleFun

would return a function itself then yes. But most probably

getOrPut("first arg", ::sampleFun)

or

getOrPut("first arg") { sampleFun(it) }

@Alowaniak, yes, you are right, if

sampleFun

return function itself, but I think it is maybe confusing to @Tuang.

yeah, it’s a little bit confusing me,, if u have another idea please do share me @Drasko Saric

Check this out: https://pastebin.com/8eZShj1W

thanks @Drasko Saric I’ll be check

I am glad to hear that. Now when you understand this, try to understand the thing that @Alowaniak said, i.e.

getOrPut("first arg", sampleFun("first arg"))

would make sense only when

sampleFun(..)

would return a function. 🙂

Sure thing

@Tuang, just to answer more precisely to your original question, what follows

handler

is just a type declaration (like

String

), only that it’s a function type, so it accepts any function reference. The function type specifies its input and output types. So like others showed above, that parameter can accept a function/method reference or a lambda.

Also you might want to play around with using functions as variables

val myPrint: (x: Any) -> Unit = ::println

myPrint("foo")