Hey folks I had an idea for predicated scope functions. Wondering if anyone has proposed these befor...

# language-proposals

[Jesse Gottlieb]

Hey folks I had an idea for predicated scope functions. Wondering if anyone has proposed these before or if they are a good candidate for a KEEP. The idea is to add applyIf, applyUnless , alsoIf , and alsoUnless to the standard lib. I chose apply and also among the various scope functions because these functions simply return the receiver object, so the return type can still be known regardless of the predicate. As a server developer, I use applyIf on builder objects quite frequently and my company has added it to an internal shared kotlin library. I suspect many kotlin devs use some version of this already.

An example would be:

inline fun <T> T.applyIf(predicate: Boolean, f: T.() -> Unit) = apply {
  if (predicate) f()
}

val myPlanBuilder = MyPlan.newBuilder()

myObjectBuilder.applyIf(isSunnyOutside) {
  addPlanLineItem(goGetIceCream)
}

[hfhbd]

This idea/feature request was requested multiple times in the past.
Personally, I don’t see a advantage compared to a simple if: if is easier to read, easier to understand and easier to debug. I try to not overuse scope functions for these reasons. Don’t be afraid of if and additional variables.

[ephemient]

definitely not going to be in stdlib before https://youtrack.jetbrains.com/issue/KT-32993

[Jesse Gottlieb]

ok, understood!