避免强转

总得说点什么,🙂

import Foundation

class Person {
    var name = ""
}

class Teacher: Person {
    var age = 0
}

let teacher: Person = Teacher()

// 强转使用
let age = (teacher as! Teacher).age

// 避免强转
if let tea = Optional(teacher) as? Teacher {
    print(tea.age)
}

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