[Swift] Safe Index

extension Array {
    subscript (safe index: Int) -> Element? {
    	// iOS 9 or later
        return indices ~= index ? self[index] : nil	
        // iOS 8 or earlier
        // return startIndex <= index && index < endIndex ? self[index] : nil
        // return 0 <= index && index < self.count ? self[index] : nil
    }
}

let list = [1, 2, 3]
list[safe: 4] // nil
list[safe: 2] // 3

 

출처: http://minsone.github.io/programming/check-index-of-array-in-swift