Today I looked for something like a conditional le...

# announcements

[Michael Böiers]

Today I looked for something like a conditional let or run, but found nothing. How about this - would something like it make sense in the standard library? https://pl.kotl.in/EI387hmPU

inline fun <T> T.thatIf(condition: Boolean, block: T.() -> T) = if (!condition) this else block()
inline fun <T, R> T.thatIf(condition: Boolean, default: R, block: T.() -> R) = if (!condition) default else block()

inline fun <T> T.letIf(condition: Boolean, block: (T) -> T) = if (!condition) this else block(this)
inline fun <T, R> T.letIf(condition: Boolean, default: R, block: (T) -> R) = if (!condition) default else block(this)

val ALL_TO_LOWER = true
val APPEND_SIZE = false

fun main() {
    val foo = "Foo"
        .thatIf(ALL_TO_LOWER) { toLowerCase() }
        .thatIf(APPEND_SIZE) { "$this ($length)"}

    val bar = "Bar"
        .letIf(ALL_TO_LOWER) { it.toLowerCase() }
        .letIf(APPEND_SIZE) { "$it (${it.length})"}
    
    println("$foo $bar")
}

[Youssef Shoaib [MOD]]

Couldn't "Foo".takeIf { ALL_TO_LOWER }?.run { toLowerCase() } work maybe?

[nanodeath]

fwiw I've also added extension methods that do something like this (letIf)

[Michael Böiers]

@Youssef Shoaib [MOD] No, that would return a nullable type. And I wanted to get rid of the double lambdas or the nested if. This works, but is much less readable IMHO:
"Foo".run { if (ALL_TO_LOWER) toLowerCase() else this }

[Michael Böiers]

@nanodeath Yes, maybe I should drop the fancy name and stick with one of the existing scope functions. In this case it would then be runIf. It’s possible to do it let-style, but then we end up with two `it`s :-)

[Jonathan Olsson]

It would be pretty consistent with takeIf and takeUnless if all scope functions had an if/unless equivalent. I.e. letIf, letUnless, applyIf, applyUnless, ....