0002-dependency-injection-using-property-wrappers-001.swift

struct Product {
    // ...
    let price: Double
}

class ProductsCalculator {
    private var products: [Product] = []

    func add(product: Product) {
        products.append(product)
    }

    func calculateTotal() -> Double {
        let subtotal = products.map({ $0.price }).reduce(0, +)
        return applyTaxes(to: subtotal)
    }

    private func applyTaxes(to subtotal: Double) -> Double {
        // Some weird taxes logic 😨
        subtotal * 1.21
    }
}