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This is a simple class in Kotlin that handles three basic Bingo-related functionalities: Specifying the numbers, generating a card, and calling one random element. Additionally, it should support an empty constructor, and support Discord Emoji output, in which there should be no spaces between any elements. I personally think drivers that use this class should do their own error handling.

I'd like suggestions on how to make this more in line with Kotlin standards, e.g. idioms, code style, whether or not I should delegate error handling to drivers, alternate/more readable approaches to certain subtasks...

Edit: I have changed the code to add an additonal constructor that specifies the delimiting char between elements.

import kotlin.random.Random
class Bingo() {
 var num = (1..75).map { if (it < 10) " $it " else "$it " }
 var cur = num.associateBy({ num.indexOf(it) }, { it }).toMutableMap()
 var delim = " ∅ "
 var max = 2
 var header = "B I N G O"
 enum class Column {
 B,
 I,
 N,
 G,
 O,
 Empty
 }
 /**
 * It is expected that the number of elements ≥ 25 and is divisible by 5
 */
 constructor(nums: String, spl: Char) : this() {
 val rem = nums.substringAfter(spl).split(spl).toMutableList()
 while (rem.contains("")) rem.remove("")
 do rem.remove(rem.random()) while (rem.size % 5 != 0)
 if (rem.size < 25) return
 num = rem; delim = nums.substringBefore(spl)
 if (num[0][0] != ':') {
 num = num.sortedBy { it.length }.toMutableList()
 max = num.last().length
 num = num.map { " ".repeat(max - it.length) + it + " " }
 delim = " ".repeat(max - delim.length) + delim + " "
 header = ""
 for (i in (0..4)) header += "" + Column.values()[i] + " ".repeat(max)
 } else {
 header = ":regional_indicator_" + Column.values()[0].toString().lowercase()
 //Reg. indicators often turn into flags without spaces
 for (i in (1..4)) header += " :regional_indicator_" + Column.values()[i].toString().lowercase()
 }
 cur = num.associateBy({ num.indexOf(it) }, { it }).toMutableMap()
 }
 constructor(nums: String): this(nums, '@')
 fun card(): Array<Array<String>> {
 val ret = Array(5) { Array(5) { "" } }
 var index: Int
 val done = mutableListOf<Int>()
 for (i in (1..5))
 for (j in (1..5)) {
 if (i == j && j == 3) {
 ret[2][2] = delim
 continue
 }
 do {
 index = Random.nextInt(num.size / 5 * (j - 1), num.size / 5 * j)
 } while (done.contains(index))
 ret[i - 1][j - 1] = num[index]
 done.add(index)
 }
 return ret
 }
 fun call(): Pair<Column, String> {
 if (cur.isEmpty()) return Pair(Column.Empty, "")
 var index: Int
 do index = Random.nextInt(num.size) while (cur[index] == null)
 val list = cur[index]!!.trim()
 cur.remove(index)
 return Pair(Column.values()[index / (num.size / 5)], list)
 }
}
```