0002-dependency-injection-using-property-wrappers-003.swift

protocol TaxesCalculatorType {
    func applyTaxes(to subtotal: Double) -> Double
}

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

class TaxesCalculatorB: TaxesCalculatorType {
    func applyTaxes(to subtotal: Double) -> Double {
        // Some weird taxes logic 😨
        subtotal * 1.41
    }
}

class ProductsCalculator {
    private let taxesCalculator: TaxesCalculatorType = TaxesCalculatorA()

    // ...

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