fmo91

enum Dependencies {
    // ...
    final class Container {
        // ...
        func register(_ dependency: Any, for key: Dependencies.Name = .default) {
            dependencies.append((key: key, value: dependency))
        }
        
        func resolve<T>(_ key: Dependencies.Name = .default) -> T {
            return (dependencies

fmo91

// We will create an enum as a namespace
enum Dependencies {
    // The same pattern that NotificationCenter's Name struct
    // follows.
    struct Name: Equatable {
        let rawValue: String
        static let `default` = Name(rawValue: "__default__")
        static func == (lhs: Name, rhs: Name) -> Bool { lhs.rawValue == rhs.rawValue }   
    }

fmo91

struct Person {
    let name: String
}

struct People {
    // This empty array will be the wrappedValue in the init.
    @Sorted(by: { $0.name < $1.name }) var items: [Person] = [] 
}

var people = People()

fmo91

// @propertyWrapper annotation makes this
// struct a property wrapper.
// It will be a generic struct because we will make
// it work with any kind of value type.
@propertyWrapper
struct Sorted<T> {
    // Internally, we will store the actual value of
    // the array in this property
    private var value: [T]

fmo91

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

fmo91

class ProductsCalculator {
    private let taxesCalculator: TaxesCalculatorType

    // ...

    init(taxesCalculator: TaxesCalculatorType) {
        self.taxesCalculator = taxesCalculator
    }

    func calculateTotal() -> Double {

fmo91

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

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

fmo91

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

class ProductsCalculator {
    private let taxesCalculator = TaxesCalculator()

fmo91

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

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

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

fmo91

final class ViewController: UIViewController {
    
    // MARK: - Views -
    @IBOutlet private weak var firstNumberTextField: UITextField!
    @IBOutlet private weak var secondNumberTextField: UITextField!
    @IBOutlet private weak var operationTextField: UITextField!
    @IBOutlet private weak var resultLabel: UILabel!
    
    private var operationPickerView: UIPickerView!