Learn notes from scratch (day 51)--extended constructors

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When you extend a type, you can also add a new constructor. Value types differ from reference type extensions. Value types include types other than classes, primarily enumeration types and struct types.  

Value type extension constructors

Example of a constructor defined in an extended struct type:

struct rectangle {                    var width : double    var height  : double        init (width : double, height  : double)  {        self.width   =  width        self.height  = height     } }extension rectangle {        // Defines the extension type of rectangle     init (length : double)  {            self.init (width : length, height :length)      }} var rect = rectangle (width: 320.0, height : 480.0)   //calls the constructor of two arguments, which is provided by the original type, ReThe Ctangle type is already an extension type print ("Rectangle: \ (rect.width) x \ (rect.height)")  var square =rectangle (length:  500.0)     //invokes the constructor of a parameter, which is the type of extension provided by the print ("Square: \ (square.width) x \ ( Square.height) ")

Self.init is a constructor that calls two parameters of the original type.

References type extension Constructors

Example of defining constructors in an extension class:

class person {                    var name : string    var age :  int    func description ()  -> String {         return  "\ (name)   Age is:  \"     }     init  (Name : string, age : int)  {         self.name = name        self.age  =  age    }} extension Person {            //defines the extension type of the person class     convenience init  (name :  string)  {    //Convenient constructor         self.init ( Name : name,&nbsP;AGE : 8)         }} let p1 = person ( name : "Mary")    //calls the constructor of the two parameter, which is provided by the original type, when the person type is already an extension type. Print ("Person1 : \ (P1.description ())") Let p2 = person (name : "Tony",  age  : 28)//The constructor that invokes a parameter creates a person instance, which is provided by the extension type. Print ("Person2 : \ (P2.description ())")

Code Self.init (Name:name, Age:8) invokes the specified constructor proxy section of the construction task.

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Learn notes from scratch (day 51)--extended constructors