Design Patterns: Visitor in Swift – Harness the Power of Abstraction

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Design Patterns: Harnessing the Power of Abstraction with Visitor in Swift

Design patterns are an integral part of software engineering, and they help developers create more robust and efficient code. In this article, we will explore one of the most popular design patterns, the Visitor Pattern, and how it can be used to write better code in the Swift programming language.

The Visitor Pattern is a behavioral design pattern that separates an algorithm from an object structure on which it operates. It allows us to add new operations to existing objects without modifying their structure. As a result, we can make our code more extensible and maintainable.

In Swift, the Visitor Pattern can be implemented using the protocol-oriented programming approach. This means that instead of using classes, we can use protocols to define the structure of our objects. We then define a visitor protocol that takes in the objects’ protocols as parameters. The visitor protocol should also define the operations to be performed on the objects.

Let’s take a look at an example to see how this works. Let’s say we have two structs, Car and Motorcycle, that conform to the Vehicle protocol. Both of them have a “drive” method that moves them forward. We can use the Visitor Pattern to add a new operation to both of these structs without modifying their structure.

First, let’s define the Vehicle protocol: 

protocol Vehicle {
    func drive()
}

Next, let’s define the two structs that conform to the protocol: 

struct Car: Vehicle {
    func drive() {
        print("Car is driving")
    }
}

struct Motorcycle: Vehicle {
    func drive() {
        print("Motorcycle is driving")
    }
}

Now, let’s define the visitor protocol. It should take in the Vehicle protocol as a parameter and define the new operation we want to add: 

protocol VehicleVisitor {
    func visit(vehicle: Vehicle)
}

extension VehicleVisitor {
    func turnOnLights(vehicle: Vehicle) {
        print("Turning on lights")
    }
}

Finally, let’s create an instance of the visitor and call its “turnOnLights” method on the Car and Motorcycle structs: 

let car = Car()
let motorcycle = Motorcycle()

let vehicleVisitor = VehicleVisitor()
vehicleVisitor.turnOnLights(vehicle: car)
vehicleVisitor.turnOnLights(vehicle: motorcycle)

The output of the above code is:

Turning on lights
Turning on lights

As you can see, the Visitor Pattern allowed us to add a new operation to both the Car and Motorcycle structs without modifying their structure. This makes our code more extensible and maintainable.

In summary, the Visitor Pattern is a powerful design pattern that allows us to separate an algorithm from an object structure on which it operates. It allows us to add new operations to existing objects without modifying their structure, making our code more extensible and maintainable. In Swift, the Visitor Pattern can be implemented using the protocol-oriented programming approach. We can define a visitor protocol that takes in the objects’ protocols as parameters and define the operations to be performed on the objects.

The Visitor Pattern is a great tool for creating more robust and efficient code in Swift, and it’s worth learning more about. Hopefully this article has given you an overview of how the Visitor Pattern works and how it can be used to write better code in Swift.

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