Inheritance / override / final / super

Since:		Swift 1.0(2014)

A Swift class can inherit from another class. Use the override keyword to override a method or property defined in a parent class.

Syntax

// Base class
class ParentClass {
    func method() { }
    var property: Type { get }
}

// Inheritance
class ChildClass: ParentClass {
    // Override
    override func method() {
        super.method() // Call the parent implementation
        // Additional logic
    }

    // Method that cannot be overridden further
    final func finalMethod() { }
}

Syntax Overview

Syntax	Description
class Child: Parent { }	Defines a child class that inherits from the parent class.
override func / var	Overrides a method or property defined in the parent class.
super.method()	Calls the parent class's implementation.
final class	Defines a class that cannot be subclassed.
final func / var	Defines a method or property that cannot be overridden.

Sample Code

sample_inheritance_override.swift

// Base class
class Employee {
    var name: String

    init(name: String) {
        self.name = name
    }

    func role() -> String {
        return "On assignment"
    }

    func describe() -> String {
        return "\(name): \(role())"
    }
}

// Inheritance and override
class FullTimeEmployee: Employee {
    override func role() -> String {
        return "Working on projects in the dev department"
    }

    // Additional method
    func report() {
        print("\(name) created a progress report")
    }
}

class Manager: Employee {
    var department: String

    init(name: String, department: String) {
        self.department = department
        super.init(name: name) // Always call super.init
    }

    override func role() -> String {
        return "Leading the team as manager"
    }

    override func describe() -> String {
        let base = super.describe()
        return "\(base) (\(department))"
    }
}

let member_x = FullTimeEmployee(name: "member_x")
let staff_a = Manager(name: "staff_a", department: "Dev Department")

print(member_x.describe())
print(staff_a.describe())
member_x.report()

// Polymorphism
let employees: [Employee] = [member_x, staff_a, FullTimeEmployee(name: "member_y")]
for employee in employees {
    print(employee.describe())
}

Running the above produces the following output:

swift inheritance_override.swift
member_x: Working on projects in the dev department
staff_a: Leading the team as manager (Dev Department)
member_x created a progress report
member_x: Working on projects in the dev department
staff_a: Leading the team as manager (Dev Department)
member_y: Working on projects in the dev department

Notes

Swift supports only single inheritance — a class cannot have more than one parent class. When a subclass overrides an initializer, it must call super.init().

Marking a class, method, or property with final prevents it from being overridden or subclassed, which can also improve performance. Defining a method with the same name as a parent class method without the override keyword causes a compile error. Always use the override keyword when intentionally overriding.

For details on property types, see Stored Properties / Computed Properties / lazy.

If you find any errors or copyright issues, please contact us.

Home