In c/c++, 0 and null are often used to represent no value, and optional was developed in swift to replace this risky practice
Both ? and ! can be used to define optional variables
! Can also be used to force unpacking, but use! The defined optional means that there must be a value, use! That is to omit those unnecessary checks, but there is a risk
var x: Int? = 8
1. Poor usage
x！+ 2
2, the relatively poor processing method
if x ！= nill {
x = x! + 1
}
3. Recommended handling method
var x: Int? = 8
if let myNumber = x {
myNumber + 1
}
highScore = loadedScore != nil ? loadedScore! : 0
highSrore = loadedScore ?? 0