Learning Swift from scratch (Day 42)--constructor call rule

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You can use the constructor proxy in a constructor to help complete some of the construction work. Class constructor proxies are divided into horizontal and upward proxies, which can only occur inside the same class, and this constructor is called a convenience constructor. An up-agent occurs in the case of inheritance, in which the parent class constructor is called to initialize the stored property of the parent class, which is called the specified constructor, during the child class construction.  

Constructor Call rules

Person and the Student Class Example:

Class person {    var name: string    var age :  int        func description ()  -> String  {        return  "\ (name)   Age is:  \"      }    convenience init  ()  {         //Convenient constructor         self.init (name:  "Tony")          self.age = 18    }     convenience init  (name: string)  {//convenient constructors          Self.init (name: name, age: 18)     }    init  (name:  string, age: int) {       //Specify constructors          self.name = name        self.age  = age     }} class Student: Person {    var school:  string    init  (name: string, age: int,school: string)  {        //the specified constructor         self.school  = school        super.init (name: name, age:  Age)     }    convenienceoverride init  (name: string,age :  int)  {//Convenient constructor         self.init (name: name, age:  age, school:  "Tsinghua University")     }} let student = student () Print ("Student:  \ (Student.description ())")

Calls between constructors form a chain of constructor functions.

Swift rules that restrict proxy calls between constructors are 3 bar, as shown below.

• specifies that the constructor must call the specified constructor of its immediate parent class. visible from the diagram, the ④ number in Student specifies that the constructor calls the ③ number in the person specified by the constructor.

• the convenience constructor must call other constructors defined in the same class. as seen from the diagram, the ⑤ in Student facilitates constructors to call the ④ number in the same class to facilitate constructors, person The ① number in the convenient constructor calls the ② number in the same class to facilitate the constructor.

• the convenience constructor must eventually end with a call to a specified constructor function. as seen from the diagram, the ⑤ in Student facilitates the constructor to call the ④ number in the same class to specify the constructor, the person The ② number in the convenient constructor calls the ③ number in the same class to specify the constructor.

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Learning Swift from scratch (Day 42)--constructor call rule