i want to use when expression in this kind of situ...

# getting-started

[zucen.co]

i want to use when expression in this kind of situation

when(string){
   null -> ...
   this.length>1 -> ...
   else ->
}

i resorted to this:

when{
   this==null -> ...
   this.length>1 -> ...
   else ->
}

is this idiomatic solution?

[menegatti]

btw, you can escape your code with 3 backticks (```) to make it look better

[zucen.co]

ok I will from now 🙂

[andyb]

when{
   this is Nothing -> ...
   this.length>1 -> ...
   else ->
}

Is the action of an empty String the same as a null?
If so you could rewrite it as

when{
   this is Nothing || this.length == 0-> ...
   else ->
}

[zucen.co]

ah,, no this is not a probem I was more wondering if I may call attrbute on the argument when(arg) in what i symbolicaly wrote as 'this.length'

[andyb]

Think I misunderstood the question, unfortunately this will not correspond to the subject of the when condition. To need to evaluate the branches using the name of the object outside the when block. Hope that makes sense

[zucen.co]

Ah... really aha... think is ... I was using this construct in special context

fun String?.shortened(maxLen:Int=60) = when{
    this == null -> ""
    this.length<maxLen -> this
    else -> "${this.substring(0,maxLen)}...(+${this.length-maxLen})"
}

so I thought this was in this context reference to when argument... but in fact it is this as extended target

[andyb]

That's right

[zucen.co]

So is the way I worte it, good way?

[andyb]

that should be fine, I'd just compare it to Nothing rather than null though

[zucen.co]

aha.. I will look in dept at Nothing... it is a bit new concept for me.. that Any vs Nothing and Nothing vs void 🙂

[andyb]

You might find this blog post from @natpryce helpful: http://natpryce.com/articles/000818.html

[zucen.co]

Thanks Andy

[Andreas Sinz]

@andyb how do you compare it to Nothing?

[andyb]

this is Nothing

[Andreas Sinz]

but Nothing can be Nothing? (pun not intended)

[Andreas Sinz]

null is Nothing results in false

[andyb]

val test : String? = null

    when (test) {
        is Nothing -> println("I am Nothing")
        else -> println("I am $test.")
    }

This code prints out ""I am Nothing"

[andyb]

Interestingly this code is different & prints out "I am null" which indicates that it has gone into the else condition:

val test : String? = null

when {
test is Nothing -> println("I am Nothing")
else -> println("I populated $test.")
}

[andyb]

That has really caught me out & it looks like it might be a bug

[zucen.co]

PLS 🙂 when you find out... if you will put it here 😄

[zucen.co]

But one more difference
this compiles

val alfa:String?=null
when{
    alfa == null -> print("nothing")
    alfa.length>1 -> print("${alfa.length}")
    else -> print("else")
}

this does not

when{
    alfa is Nothing -> print("nothing")
    alfa.length>1 -> print("${alfa.length}")
    else -> print("else")
}

[Andreas Sinz]

@andyb test is Nothing == false is a bug?