Design Patterns — Proxy

Today, we will talk about proxy pattern. In this pattern, proxy is an object to help us to access another object. It simply delegates real job to that object or change its behavior. The following figure depicts the roles and their relationships.

from Proxy pattern — Wikipedia

Proxy pattern is popularly used in Cocoa which even has a specific NSProxy class in it. Another example is UIApperance protocol and other relevant types.

We will continue using our car system.

protocol Car {
    func drive()
} 

class Sedan: Car {
    func drive() {
        print("drive a sedan")
    }
}

Autonomous car is so hot topic now. So let’s build our own. Actually, it’s not built from scratch but enhance our current car with self-driving system. So it has a internal car instance and delegate the driving to the car. But as an autonomous car, it controls the car automatically. Delegation and change are what a proxy does in this pattern.

class ProxyCar: Car {
    var car: Car     

    init(car: Car) {
        self.car = car
    }     

    func drive() {

        //check condition autonomous 
        car.drive()
        print("by self-driving system")
    }
}

Let’s see how to drive it.

//usage
let sedan = Sedan()
let proxyCar = ProxyCar(car: sedan)proxyCar.drive()

---

Thanks for your time. Please clap to get this article seen by more people. Please follow me by clicking Follow. As a passionate iOS developer, blogger and open source contributor, I’m also active on Twitter and GitHub.