此处构造函数参数中缺少val关键字。
如果要再次重新指定列表，可以将设为var。
在Kotlin构造函数中，如果你不定义它，它将是一个特定类的属性。所以它不可能在构造函数之外被访问。

class PayrollSystem(val list: MutableList<Employee>) {

    fun calculatePayroll(){
        //You can access it with list.someThing()
    }
}

以防有人会面临类似的任务。

fun main(args: Array<String>) {
    var index = 0
    val employees = mutableListOf(SalaryEmployee(index, "blablabla", 0))
    val x: String = "0"
    while(true) {
        print("Please enter employee name (0 to quit):")
        var input = readLine()!!.toString()
        if (input != x) {
            index++
            print("Please enter salary:")
            var wage = readLine()!!.toInt()
            employees.add(SalaryEmployee(index, input, wage))
        }
        else {
            employees.removeAt(0)
            PayrollSystem(employees).calculatePayroll()
            break;
        }
    }
}

class PayrollSystem(val list: MutableList<SalaryEmployee>) {

    val temp = list
    fun calculatePayroll(){
        temp.forEach{
            println("Employee Payroll\n================")
            println("Payroll for: ${it.id} - ${it.name}\n- Check amount: ${it.monthly_salary}\n")
        }
    }
}

class SalaryEmployee(id: Int, name: String, val monthly_salary: Int) : Employee(id, name){

    fun calculateSalary(): Int {
        return monthly_salary
    }
}

open class Employee(open val id: Int, open val name: String) {

}```