what does this ` handler: (key: K) -> V?) ` mea...

# getting-started

[Tuang]

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 ?

[diesieben07]

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

[Drasko Saric]

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.

[Tuang]

@Drasko Saric
thanks

So, how to set the parameter when I call getOrPut() function.
may be like this ?

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

[Drasko Saric]

No. Let me explain.

[Alowaniak]

if sampleFun would return a function itself then yes.
But most probably getOrPut("first arg", ::sampleFun) or getOrPut("first arg") { sampleFun(it) }

[Drasko Saric]

@Alowaniak, yes, you are right, if sampleFun return function itself, but I think it is maybe confusing to @Tuang.

[Tuang]

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

[Drasko Saric]

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

[Drasko Saric]

There are two functions with same signature, getOrPut function and function used for calling getOrPut.

[Tuang]

thanks @Drasko Saric
I’ll be check

[Tuang]

thank you very much guys,,especially @Drasko Saric
i understand now

[Drasko Saric]

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. 🙂

[Tuang]

Sure thing

[Matteo Mirk]

@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.

[Alowaniak]

Also you might want to play around with using functions as variables val myPrint: (x: Any) -> Unit = ::println myPrint("foo")