Can you explain the concept of dependency inversion and its role in system design?

Inversion of Control (IoC) is a design principle where the management of dependencies between system components is delegated to an external container or framework, rather than being created directly within the components.

Role in system design:

• Enhances modularity and testability, as components do not depend on specific implementations but receive them externally.
• Simplifies replacement and extension of components without changing the code that uses them.

Example: instead of the class creating the dependency object itself, it receives it through a constructor or setter. This allows easy substitution of implementations, for example, for testing.

protocol Service {
    func doWork()
}

class RealService: Service {
    func doWork() { print("Work completed") }
}

class Client {
    let service: Service
    init(service: Service) {
        self.service = service
    }
}

let service = RealService()
let client = Client(service: service)

Here, Client does not create RealService itself but receives it from outside — this is the essence of inversion of control.