Basic class with a get/set parameter

Office.swift

import Cocoa

class thisOffice {
    
    var currentUsers: Int
    var totalSpaces : Int
    
    init(currentUsers: Int, totalSpaces: Int) {
        self.currentUsers = currentUsers
        self.totalSpaces = totalSpaces
    }
    
    var freeSpaces: Int {
    
        get {
            return totalSpaces - currentUsers
        }
    
        set {
           
            self.currentUsers = totalSpaces - newValue
            
        }
    
    }
    
}

var currentOffice = thisOffice(currentUsers: 4, totalSpaces: 6);

currentOffice.freeSpaces
currentOffice.freeSpaces = 1
currentOffice.currentUsers