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 lt T gt T elseIf predicate T gt Boolean supplier gt T T = when predicate gt supplier invoke else gt 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

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

09/27/2019, 1:04 PM

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

☝️ 4

or even

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

☝️ 1

Andreas Unterweger

09/27/2019, 1:07 PM

ok....that looks good

karelpeeters

09/27/2019, 1:08 PM

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

➕ 3

Andreas Unterweger

09/27/2019, 1:09 PM

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

Dominaezzz

09/27/2019, 1:12 PM

"sss".orEmpty { "other" }

karelpeeters

09/27/2019, 1:13 PM

Isn't that for converting

null

""

Dominaezzz

09/27/2019, 1:13 PM

Hmm, lemme confirm.

😅 I meant

"sss".ifEmpty { "other" }

Andreas Unterweger

09/27/2019, 1:16 PM

well these are great, but specific to string

Dominaezzz

09/27/2019, 1:27 PM

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

Andreas Unterweger

09/27/2019, 1:34 PM

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

09/27/2019, 4:13 PM

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" }

😲 1

gildor

09/30/2019, 2:29 AM

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("...")

➕ 1

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

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