“Mediator” design pattern in swift | by Harald Bregu | Feb, 2023

The Mediator design pattern is a behavioral pattern that allows objects to communicate with each other through a mediator object instead of directly interacting with each other.

Let’s use the example of a real estate or car transaction to illustrate the roles of the seller, buyer, and mediator agent:


class Person {
 var name: String

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

protocol Mediation {
 func completeTransaction(seller: Seller)
}

class PersonMediator: Person, Mediation {
 private var counterParts = [Person]()

 var offer: Double = 0.0
 var acceptedOffer: Bool = false

 func register(counterpart: Person) {
 counterParts.append(counterpart)
 }

 func completeTransaction(seller: Seller) {
 print(seller.message)
 }
}


class CounterPart: Person {
 var mediator: PersonMediator

 init(name: String, mediator: PersonMediator) {
 self.mediator = mediator
 super.init(name: name)
 }
}

class Buyer: CounterPart {
 override init(name: String, mediator: PersonMediator) {
 super.init(name: name, mediator: mediator)
 }

 func sendOffer(_ offer: Double) {
 print("I am sending an offer of \(offer) dollars")
 mediator.offer = offer
 }
}

class Seller: CounterPart {
 override init(name: String, mediator: PersonMediator) {
 super.init(name: name, mediator: mediator)
 }

 var message: String {
 if mediator.offer > 190_000 {
 return "I will accept your offer of \(mediator.offer) dollars"
 }
 return "I will not accept your offer of \(mediator.offer) dollars"
 }
}

var mediator = PersonMediator(name: "Agent Smith")

var buyer = Buyer(name: "Marina Mitchell", mediator: mediator)
mediator.register(counterpart: buyer)

var seller = Seller(name: "Dillan Grimes", mediator: mediator)
mediator.register(counterpart: seller)

buyer.sendOffer(100_000)

mediator.completeTransaction(seller: seller)

buyer.sendOffer(200_000)

mediator.completeTransaction(seller: seller)

If you observe, the buyer and seller do not have a direct connection, but instead are managed by the mediator. In this case, we have utilized two design patterns — the Abstract Factory pattern to create Counter Parts and Agents, and the Mediator pattern to manage their interactions.

If you are interested in learning more about design patterns in Swift, you can check out my GitHub repository, where I have provided examples and explanations of various design patterns.

Thanks!

“Mediator” design pattern in swift | by Harald Bregu | Feb, 2023 | Medium