Swift's optional selectable values

• Optionalis a major feature of Swift and the most confusing problem for swift beginners
• When a variable is defined, the variable is represented if it is specified 可选的可以有一个指定类型的值，也可以是 nil
• When defining a variable, add one after the type ? to indicate that the variable is optional
• The default value of a variable's optional option isnil
• Constant options have no default values and are primarily used to set initial values in constructors for constants

//: num 可以是一个整数，也可以是 nil，注意如果为 nil，不能参与计算let num: Int? = 10

• If the Optional value is nil not allowed to participate in the calculation
• Only 解包(unwrap) then can we participate in the calculation
• Add one after the variable to ! forcibly unpack the package

Note: You must ensure that the value after unpacking is not nil, otherwise it will be an error

//: num 可以是一个整数，也可以是 nil，注意如果为 nil，不能参与计算let num: Int? = 10//: 如果 num 为 nil，使用 `!` 强行解包会报错let r1 = num! + 100//: 使用以下判断，当 num 为 nil 时，if 分支中的代码不会执行if let n = num { let r = n + 10}

Common errors

unexpectedly found nil while unwrapping an Optional value

Translation

在[解包]一个可选值时发现 nil

??Operator

• ??The operator can be used to determine 变量/常量 if the numeric value is nil , or if it is, use the following value instead
• Simplifies code writing when using Swift development ??
• Equivalent to three mesh operation

let num: Int? = nillet r1 = (num ?? 0) + 10print(r1)

Swift's optional selectable values