How does one deconstruct a List passed into a Kotlin function?
Problem:
Rather than passing a complex list of parameters to a function, I wanted to pass in a List and deconstruct it in the function body. The code below does not work, so I reverted to extracting each variable (Simplified code example below) – recommendations?
val (h1, m1, s1, h2, m2, s2) = timeData
Question:
What is the correct way to deconstruct the timeData into a component set of values?
Simplified Code Example:
import java.util.Scanner
const val HOURS = 3600
const val SECONDS = 60
fun secondsBetweenTwoMoments(timeData: List<Int>): Int {
require(timeData.size == 6) { "List must have exactly 6 elements" }
val h1 = timeData[0]
val m1 = timeData[1]
val s1 = timeData[2]
val h2 = timeData[3]
val m2 = timeData[4]
val s2 = timeData[5]
// Convert moment 1 and 2 to seconds
val seconds1 = h1 * HOURS + m1 * SECONDS + s1
val seconds2 = h2 * HOURS + m2 * SECONDS + s2
return seconds2 - seconds1
}
fun main() {
val scanner = Scanner(System.`in`)
val inputs = mutableListOf<Int>()
repeat(6) {
inputs.add(scanner.nextInt())
}
val seconds = secondsBetweenTwoMoments(inputs)
println(seconds)
}
to summarise, "Sir, I came across an interesting piece of magic…" (Chuckle)
>Solution :
You have simply hit the limit of the number of destructuring operator functions the standard library has defined for a List. You can add one more, and then the destructuring code will work:
operator fun <T> List<T>.component6(): T = get(5)
As for why they only built in destructuring up to 5 elements, I think it’s because beyond that it’s getting to be a little bit fragile/unreadable to use and you might want to consider using a specialized data class instead of a List.
I’m not sure why you mention casting, since there is no casting occurring in your code.