Learn Swift from scratch Learning Note (day)--final keywords

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used in the definition of a class Final keyword to declare classes, properties, methods, and subscripts. final declared classes cannot be inherited,andfinal declared properties, methods, and subscripts cannot be overridden.

Let's look at an example:

The final class person {//declaration is final, stating that it cannot be inherited         var  name: String        final var age: Int     //-Defined Age attribute         final func description ()  -> string {  //defining Description Instance methods          return  "\ (name)   Age is:  \"     }         final class func printclass ()  -> ()  {  //define Printclass static methods          print (  "person  printing ...")     }         init  (Name: string, age: int) {         self.name = name         Self.age  = age    }} class student: person {                              //compilation Error         var school: string         convenience init ()  {         self.init (name:  "Tony", age: 18,school:  "Tsinghua University")              init  (name: string, age: int,school:  String)  {        self.school = school         super.init (name: name, age: age)     }         override func description ()  -> String{          //compilation error     //attempting to override description instance method          print ("Parent class print  \ (Super.description ())")          return  "\ (name)   Age is:  \,  School:  \ (school). "    }        override class func  Printclass ()  -> () {      //compilation error   //attempted to override Printclass static method          print (  "student  printing ...")     }         override var age: Int {                          //Compile error//attempt to override age property     get {         return super.age    }     set {        super.age = newvalue < 8  ? 8: newvalue    }    }}

definition Student class, and declared as Person Child class, the following compilation error is reported:

Inheritance from a finalclass ' person '

defined by Age properties are also Final , then in an attempt to rewrite Age property, the following compilation error is reported:

var overrides a ' final ' var

definition Description instance method, which is declared as Final , then in an attempt to rewrite Description instance method, the following compilation error is reported:

Instance method Overridesa ' final ' Instance method

definition Printclass static method, which is declared as Final , then in an attempt to rewrite Printclass when a static method is used, the following compilation error is reported:

Class method overrides a ' final ' class method

Use Final can control our classes are limited inheritance, especially in the development of some commercial software, when appropriate to add Final restrictions are necessary.

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Learn Swift from scratch Learning Note (day)--final keywords