swift-final keyword-b

Use the final keyword in the definition of a class 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:

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Final class Person {//declared as final, indicating that it cannot be inherited

var name:string

Final var age:int//Defined Age property

Final func description ()-> String {//Define Description instance method

Return "\ (name) age is: \ (aged)"

}

Final class Func Printclass ()-> () {//define Printclass static method

Print ("Person prints ...")

}

Init (name:string, Age:int) {

self.name = name

self.age = Age

}

}

Class Student:person {//Compile 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 {//Compile error//attempt to override Description instance method

Print ("Parent class printing \ (Super.description ())")

Return "\ (name) is: \ (age), school: \ (school). "

}

Override class Func Printclass ()-> () {//Compile error//attempt 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

}

}

}

When you define the student class and declare it as the person subclass, the following compilation error is reported:

Inheritance from a finalclass ' person '

The definition of the Age property is final, and the following compilation error is reported when attempting to override the attribute:

var overrides a ' final ' var

Defining the Description instance method, which is declared final, the following compilation error is reported when attempting to override the description instance method:

Instance method Overridesa ' final ' Instance method

Defining the Printclass static method, which is declared final, the following compilation error is reported when attempting to override the Printclass static method:

Class method overrides a ' final ' class method

Using final can control our classes being limited inheritance, especially when developing some commercial software, it is necessary to add the final limit appropriately.

swift-final keyword-b