hello everyone, i am looking for a control functio...

# announcements

[Andreas Unterweger]

hello everyone, i am looking for a control function elseIf
it should allow me to take another value if the predicate does return true. i implemented the following extension function:

inline fun <T> T.elseIf(predicate: T.() -> Boolean, supplier: () -> T) : T =
        when {
            predicate() -> supplier.invoke()
            else -> this
        }

its called like val i = "ssss".elseIf({isEmpty()}) {"other"}
which feels very clumsy. can i optimize the syntax more? or arent there already alternatives in kotlin? or maybe im just missing the easy solution?

[Oleg Yukhnevich]

val i = "ssss".takeIf { it.isEmpty() } ?: "other"

[Oleg Yukhnevich]

or even "ssss".takeIf(String::isEmpty) ?: "other"

[Andreas Unterweger]

ok....that looks good

[karelpeeters]

val s = "ssss"
if (s.isEmpty()) "other" else s

[Andreas Unterweger]

thx..that the obvious one...but i prefer takeIf...but still think its not optimal

[Dominaezzz]

"sss".orEmpty { "other" }

[karelpeeters]

Isn't that for converting null to ""?

[Dominaezzz]

Hmm, lemme confirm.

[Dominaezzz]

😅 I meant "sss".ifEmpty { "other" }

[Andreas Unterweger]

well these are great, but specific to string

[Dominaezzz]

I think these are only useful when they are specific. Otherwise it's harder to read.

[Andreas Unterweger]

well my function is not so bad, but unfortunately calling it looks strange but its generic File("").elseIf({!exists()}, {File("other)}) otherwise olegs takeif seems the best

[molikuner]

Even though I would prefer the plain `if`:

infix fun <T> T.unless(predicate: T.() -> Boolean) = this to predicate
infix fun <T> Pair<T, T.() -> Boolean>.then(supplier: () -> T) = when {
    first.second() -> supplier()
    else -> first
}

"ssss" unless { isEmpty() } then { "other" }

[gildor]

I often use File with takeIf, and it works file, also more flexible, because you part after ?: also can be return, break etc:

File("").takeIf(File::exists) ?: File("other")
// or 
File("").takeIf(File::exists) ?: return
// or
File("").takeIf(File::exists) ?: error("...")

[gildor]

If you very often need this pattern with alternative File, I would just write File.ifNotExtists extension, like String.ifEmpty but I would do this only if I need it multiple times, for single usage takeIf is just fine for me