Singleton.swift

class DataItem {
    
    enum ItemType : String {
        case Email = "Email Address"
        case Phone = "Telephone Number"
        case Card  = "Credit Card Number"
    }
    
    var type:ItemType
    var data:String
    
    init(type:ItemType, data:String) {
        self.type = type
        self.data = data
    }
}

final class Logger {
    private var data = [String]()
    
    private init() {
        
    }
    
    func log(msg:String) {
        data.append(msg)
    }
    
    func printLog() {
        for msg in data {
            print("Log; \(msg)")
        }
    }
}

let globalLogger = Logger()

class BackupServer {
    let name:String
    private var data = [DataItem]()
    
    init(name:String) {
        self.name = name
        globalLogger.log("Created new server \(name)")
    }
    
    func backup(item:DataItem) {
        data.append(item)
        globalLogger.log("\(name) backed up item of type \(item.type.rawValue)")
    }
    
    func getData() -> [DataItem] {
        return data
    }
}

var server = BackupServer(name: "Server#1")
server.backup(DataItem(type: DataItem.ItemType.Email, data: "[email protected]"))
server.backup(DataItem(type: DataItem.ItemType.Phone, data: "[email protected]"))
globalLogger.log("Backed up 2 items to \(server.name)")

var other = BackupServer(name: "Server#2")
other.backup(DataItem(type: DataItem.ItemType.Card,  data: "[email protected]"))
globalLogger.log("Backed up 1 items to \(other.name)")
globalLogger.printLog()