Замена локальных изменяемых переменных на неизменяемый параметр функции (v0.0.0)

    fun parseInt(str: String): ParseResult {
        var res = 0
        var negative = false
        var firstInvalidCharIdx = -1
        str.forEachIndexed { idx, char ->
            when (char) {
                '-' if idx == 0 -> negative = true
                in '0'..'9' -> res = res * 10 + char.digitToInt()
                else -> firstInvalidCharIdx = idx
            }
        }

        if (firstInvalidCharIdx != -1) {
            return ParseResult.Failure(firstInvalidCharIdx, str[firstInvalidCharIdx])
        }

        if (negative) {
            res = -res
        }

        return ParseResult.Success(res)
    }

data class ParsingData(
    val digits: List<Int> = emptyList<Int>(),
    val negative: Boolean = false,
    val firstInvalidChar: Int = -1
)

    fun parseInt3(str: String): ParseResult {
        val stringData = str.foldIndexed(ParsingData()) { idx, data, char ->
            when (char) {
                '-' if idx == 0 -> data.copy(negative = true)
                in '0'..'9' -> data.copy(digits = data.digits + char.digitToInt())
                else -> data.copy(firstInvalidChar = idx)
            }
        }

        return when {
            stringData.firstInvalidChar != -1 -> ParseResult.Failure(
                stringData.firstInvalidChar,
                str[stringData.firstInvalidChar]
            )

            stringData.negative -> ParseResult.Success(stringData.digits.fold(0) { acc, d -> acc * 10 + d } * -1)
            else -> ParseResult.Success(stringData.digits.fold(0) { acc, d -> acc * 10 + d })
        }
    }