CODESAMPLE

Decorator - Swift

Decorator Swift

The Decorator pattern dynamically adds responsibilities to an object. It provides a flexible alternative to subclassing for extending functionality. Instead of inheriting from a base class to add features, we wrap the original object with one or more decorator objects, each adding a specific behavior.

This Swift implementation uses protocol-oriented programming, which is highly idiomatic. The Coffee protocol defines the core functionality. BaseCoffee conforms to this protocol, providing a basic implementation. Decorator also conforms to Coffee, holding a Coffee instance and delegating to it. Concrete decorators like MilkDecorator and SugarDecorator add their specific behaviors before delegating to the wrapped Coffee. This avoids modifying the original Coffee class and allows for runtime composition of features.

protocol Coffee {
    var cost: Double { get }
    var description: String { get }
}

class BaseCoffee: Coffee {
    let description: String
    let cost: Double

    init(description: String, cost: Double) {
        self.description = description
        self.cost = cost
    }
}

class CoffeeDecorator: Coffee {
    let coffee: Coffee

    init(coffee: Coffee) {
        self.coffee = coffee
    }

    var cost: Double {
        return coffee.cost
    }

    var description: String {
        return coffee.description
    }
}

class MilkDecorator: CoffeeDecorator {
    override var cost: Double {
        return super.cost + 0.5
    }

    override var description: String {
        return super.description + ", with milk"
    }
}

class SugarDecorator: CoffeeDecorator {
    override var cost: Double {
        return super.cost + 0.2
    }

    override var description: String {
        return super.description + ", with sugar"
    }
}

// Example Usage
let simpleCoffee = BaseCoffee(description: "Simple coffee", cost: 2.0)
let milkCoffee = MilkDecorator(coffee: simpleCoffee)
let sugaryMilkCoffee = SugarDecorator(coffee: milkCoffee)

print(sugaryMilkCoffee.description) // Output: Simple coffee, with milk, with sugar
print(sugaryMilkCoffee.cost) // Output: 2.7