What is the final class in Swift?

Posted on 27 May 2023 . 1 min read

In Swift, the final keyword is used to indicate that a class, method, or property cannot be overridden or subclassed. When you declare a class as final, it means that it's the end of the inheritance chain for that class, and it cannot be subclassed further.

Final Class:

final class MyClass {
    // Class definition
}

By marking MyClass as final, you're explicitly stating that no other class can inherit from it. This can be beneficial in several scenarios:

Preventing Subclassing: If you have a class whose design or behavior should not be modified or extended, marking it as final ensures that its functionality remains intact and cannot be altered by subclasses.
Performance Optimization: The compiler can perform certain optimizations on final classes and methods because it knows they cannot be overridden.

Usage:

final class Vehicle {
    // ...
}

// This will produce an error, as 'Car' cannot inherit from a 'final' class 'Vehicle'
class Car: Vehicle {
    // ...
}

If you mark class final, it means that it's the end of the inheritance chain for that class, and it cannot be subclassed further. If you try to implement inheritance it will produce an error, as Carcannot inherit from a finalclass Vehicle.

Final Methods and Properties:

In addition to classes, you can also mark individual methods and properties as final to prevent overriding:

class Parent {
    final func someMethod() {
        // This method cannot be overridden by subclasses
    }
    
    final var someProperty: Int {
        return 10
    }
}

class Child: Parent {
    // This will produce an error as 'someMethod()' and 'someProperty' are final
    // and cannot be overridden
}

By using final for methods and properties within a class, you ensure that these elements cannot be modified or extended by subclasses.

The bottom line

The use of final provides a way to explicitly define parts of your code that should not be overridden or extended, offering a level of control over the inheritance and customization of classes, methods, and properties in Swift.

Don’t hesitate to contact me if you have any questions or queries. Follow me on twitter @gurjitpt for any updates.

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Gurjit Singh

I’m Computer Science graduate and an iOS Engineer who writes about Swift and iOS development. Follow me for more updates:

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