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 Inspector {
    var name: String

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

    func duty() -> String {
        return "On duty"
    }

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

// Inheritance and override
class DivisionOneInspector: Inspector {
    override func duty() -> String {
        return "Investigating at Division 1"
    }

    // Additional method
    func analyze() {
        print("\(name) analyzed the Crime Coefficient with the Dominator")
    }
}

class ChiefInspector: Inspector {
    var division: String

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

    override func duty() -> String {
        return "Commanding as chief inspector"
    }

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

let kogami = DivisionOneInspector(name: "Kogami Shinya")
let ginoza = ChiefInspector(name: "Ginoza Nobuchika", division: "Division 1")

print(kogami.describe())
print(ginoza.describe())
kogami.analyze()

// Polymorphism
let inspectors: [Inspector] = [kogami, ginoza, DivisionOneInspector(name: "Tsunemori Akane")]
for inspector in inspectors {
    print(inspector.describe())
}

Running the above produces the following output:

swift inheritance_override.swift
Kogami Shinya: Investigating at Division 1
Ginoza Nobuchika: Commanding as chief inspector (Division 1)
Kogami Shinya analyzed the Crime Coefficient with the Dominator
Kogami Shinya: Investigating at Division 1
Ginoza Nobuchika: Commanding as chief inspector (Division 1)
Tsunemori Akane: Investigating at Division 1

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.

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