swift guard, if 기준정하기

swift guard, if 기준정하기

참고

- guard 참고

https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/ControlFlow.html

https://www.natashatherobot.com/swift-when-to-use-guard-vs-if/

[위 사이트 번역] http://blog.canapio.com/108?category=948003

[더 봐야할] http://radex.io/swift/guard/

[더 봐야할]https://thatthinginswift.com/guard-statement-swift/

- where 문법 참고

https://stackoverflow.com/questions/38446598/xcode-8-beta-3-expected-joining-parts-of-a-multi-clause-condition 

https://github.com/apple/swift-evolution/blob/master/proposals/0099-conditionclauses.md

thanks a lot👍