[스크랩] 스위프트 옵셔널 이해하기

http://chanlee.github.io/2015/06/14/Introduce-Swift-Optional/

https://www.appcoda.com/beginners-guide-optionals-swift/

https://devxoul.gitbooks.io/ios-with-swift-in-40-hours/content/Chapter-2/optionals.html

playground에서 예제를 똑같이 실행해 보았다.

import UIKit class Messenger {     var message1: String = "Swift is awesome"     var message2: String? } func findStockCode(company: String) -> String? {     if (company == "Apple") {         return "AAPL"     } else if (company == "Google") {         return "GOOG"     }          return nil } var stockCode:String? = findStockCode("Facebook") let text = "Stock Code - " //let message = text + stockCode! //print(message) if let tmpStock = stockCode {     let message = text + tmpStock     print(message) } if var stockCode = findStockCode("Facebook") {     let message = text + stockCode     print(message) } class Stock {     var code: String?     var price: Double? } func findStockCode2(company: String) -> Stock? {     if (company == "Apple") {         let aapl: Stock = Stock()         aapl.code = "AAPL"         aapl.price = 90.32                  return aapl     } else if (company == "Google") {         let goog: Stock = Stock()         goog.code = "GOOG"         goog.price = 556.36                  return goog     }     return nil } if let stock = findStockCode2("Apple") {     if let sharePrice = stock.price {         let totalCost = sharePrice * 100         print(totalCost)     } } if let sharePrice = findStockCode2("Apple")?.price {     let totalCost = sharePrice * 100     print(totalCost) }