Swift Optional 的四种处理方式

var ages:[Int] = []

ages.sort()

// if let
if let oldest = ages.last {
    print("this is oldest age \(oldest)")
}else {
    print("this is no oldest age")
}

// nil coalescing
let oldest = ages.last ?? 999;

// gard statement
func getOldestAge (){
    guard ages.last != nil else {
        return
    }
    print("\(oldest) is oldest age")
}
getOldestAge()

// force unwrap
let oldestAge = ages.last!
print(oldest)