Example to show prototype design pattern

prototype-pattern.swift

import Foundation

protocol Cloneable {
    func copy() -> Any
}

class Message: Cloneable {
    var to: String
    var subject: String
    
    init(to: String, subject: String) {
        self.to = to
        self.subject = subject
    }
    
    func copy() -> Any {
        return Message(to: to, subject: subject)
    }
}

class DetailedMessage: Message {
    var from: String
    init(to: String, subject: String, from:String) {
        self.from = from
        super.init(to: to, subject: subject)
    }
    
    override func copy() -> Any {
        return DetailedMessage(to: to, subject: subject, from: from)
    }
}

class MessageLogger {
    var messages:[Message] = []
    
    func logMessage(_ msg: Message) {
        guard let messageCopy = msg.copy() as? Message else { return }
        messages.append(messageCopy)
    }
    
    func processMessages(_ callback: (Message) -> Void) {
        for msg in messages {
            callback(msg)
        }
    }
}


var logger = MessageLogger()
var message = Message(to: "Joe", subject: "Hello")
logger.logMessage(message)
message.to = "Bob"

message.subject = "Free for dinner?"
logger.logMessage(message)
logger.logMessage(DetailedMessage(to: "Alice", subject: "Hi!", from: "Joe"))
logger.processMessages({msg -> Void in
    if let detailed = msg as? DetailedMessage {
        print("Detailed Message - To: \(detailed.to) From: \(detailed.from)" + " Subject: \(detailed.subject)")
    } else {
        print("Message - To: \(msg.to) Subject: \(msg.subject)")
    }
})