Swift 中打印实例输出自定义字符串

在 Swift 中如果直接通过 print 方法 打印一个类的实例多数情况会打印出实例的类名。但是如果我们想打印出具体属性值，则通过执行 CustomStringConvertible 协议并实现其协议计算属性 description 即可。
以下为具体示例代码(示例代码运行在 Xcode PlayGround)：

// 1. 首先 申明一个 Person 类
class Person {
    
    enum Gender {
        case Male
        case Female
        case Other
    }
    var firstName = ""
    var lastName = ""
    var fullName: String {
        firstName + lastName
    }
    var gender: Gender = .Other
    var age: Int = 0
    var interest: String = ""
    init(firstName: String,
         lastName: String,
         gender: Gender,
         age: Int,
         interest: String) {
        self.firstName = firstName
        self.lastName = lastName
        self.gender = gender
        self.age = age
        self.interest = interest
    }

}

2. 实例化一个 Person 对象 tom 并打印。
let tom = Person(firstName: "Tom", lastName: "Wang", gender: .Male, age: 25, interest: "basketball")
print(tom)

3. 打印结果为
__lldb_expr_84.Person

4. Person 类执行 CustomStringConvertible 协议并实现 description 计算属性。

class Person: CustomStringConvertible {
    var description: String {
        var genderString = ""
        switch gender {
        case .Female:
            genderString = "Female"
        case .Male:
            genderString = "Male"
        default:
            genderString = "Other"

        }
        return """
            Class Name [Person]
            Property:
            firstName:\(firstName)
            lastName:\(lastName)
            fullName:\(fullName)
            gender:\(genderString)
            age:\(age)
            interest:\(interest)
            """
    }
}

5. 重新运行代码则输出结果为
Class Name [Person]
Property:
firstName:Tom
lastName:Wang
fullName:TomWang
gender:Male
age:25
interest:basketball