I was just wondering why the `1` element optimizat...

# stdlib

[Edoardo Luppi]

I was just wondering why the 1 element optimization in toList

public fun <T> Array<out T>.toList(): List<T> {
    return when (size) {
        0 -> emptyList()
        1 -> listOf(this[0])
        else -> this.toMutableList()
    }
}

Looking at the listOf implementations it's mostly redundant checks and basically spawning another ArrayList, same as toMutableList

[Oleg Yukhnevich]

AFAIR there is listOf(arg) which creates specific list implementation for one element (at least on JVM)

[Sam]

https://github.com/JetBrains/kotlin/blob/1a2eac5a5f5590af940ccb4615a483b6a94e2f51/libraries/stdlib/jvm/src/kotlin/collections/CollectionsJVM.kt#L22

[Sam]

public actual fun <T> listOf(element: T): List<T> = java.util.Collections.singletonList(element)

[Edoardo Luppi]

I get this for commonMain in multiplatform

public fun <T> listOf(vararg elements: T): List<T> = if (elements.size > 0) elements.asList() else emptyList()

asList again is then actualized with ArraysUtilJVM.asList(this), which spawns an ArrayList

[Edoardo Luppi]

So it's like multiple additional calls for the same result as toMutableList, at least in KMP

[Edoardo Luppi]

Ahh wait! Maybe the IDE navigation lands on the wrong function?

[Edoardo Luppi]

Looks like the vararg alternative is prioritized.