Sample code for builder pattern in swift.

PizzaBuilder.swift

import Foundation

enum Dough: String {
    case basic
    case cheeseCrust
}

enum Topping: String, CaseIterable {
    case pepperoni
    case sausage
    case mushrooms
    case bacon
    case extraCheese
    case greenPeppers
    case blackOlives
    case onions
}

enum Size: String {
    case regular
    case large
    case family
}

// Product
class Pizza {
    private var dough: Dough = .basic
    private var toppings = [Topping]()
    private var size: Size = .regular
    
    func setDough(_ dough: Dough) {
        self.dough = dough
    }
    
    func setToppings(_ toppings: [Topping]) {
        self.toppings = toppings
    }
    
    func setSize(_ size: Size) {
        self.size = size
    }
    
    func listPizzaInfo() -> String {
        var toppingList = toppings.map { $0.rawValue }
        return "Your pizza's size is \(size.rawValue) and the dough is \(dough.rawValue), toppings are \(toppingList.joined(separator: ", "))."
    }
}

// Builder
protocol Builder {
    func reset()
    func setDough(_ dough: Dough)
    func addToppings(_ toppings: [Topping])
    func setSize(_ size: Size)
}

class PizzaBuilder: Builder {
    private var pizza = Pizza()
    
    func reset() {
        self.pizza = Pizza()
    }
    
    func setDough(_ dough: Dough) {
        self.pizza.setDough(dough)
    }
    
    func addToppings(_ toppings: [Topping]) {
        self.pizza.setToppings(toppings)
    }
    
    func setSize(_ size: Size) {
        self.pizza.setSize(size)
    }
    
    func getPizza() -> Pizza {
        let result = self.pizza
        reset()
        return result
    }
    
}

// Director
class Director {
    private var builder: Builder?
    
    func buildCheesePizza(_ builder: Builder) {
        builder.reset()
        builder.setDough(.cheeseCrust)
        builder.addToppings([.extraCheese, .mushrooms, .sausage, .greenPeppers, .blackOlives])
        builder.setSize(.regular)
    }
    
    func buildPepperoniPizza(_ builder: Builder) {
        builder.reset()
        builder.setDough(.basic)
        builder.addToppings([.pepperoni, .mushrooms, .onions, .blackOlives])
        builder.setSize(.large)
    }
}

class Client {
    func makeCheesePizza() {
        let director = Director()
        let pizzaBuilder = PizzaBuilder()
        
        director.buildCheesePizza(pizzaBuilder)
        let cheesePizza = pizzaBuilder.getPizza()
        
        print(cheesePizza.listPizzaInfo())
    }
    
    func makePepperoniPizza() {
        let director = Director()
        let pizzaBuilder = PizzaBuilder()
        
        director.buildPepperoniPizza(pizzaBuilder)
        let pepperoniPizza = pizzaBuilder.getPizza()
        
        print(pepperoniPizza.listPizzaInfo())
    }
}

let client = Client()
client.makeCheesePizza()
print()
client.makePepperoniPizza()
// Prints
// "Your pizza's size is regular and the dough is cheeseCrust, toppings are extraCheese, mushrooms, sausage, greenPeppers, blackOlives."
// "Your pizza's size is large and the dough is basic, toppings are pepperoni, mushrooms, onions, blackOlives."