Inject.swift

protocol Resolver {
    func resolve<T>(_ type: T.Type) -> T
}

class MainResolver: Resolver {
    static let shared = MainResolver()

    private var dependencies: [Any] = []

    func register<T>(_ dependency: T) {
        dependencies.append(dependency)
    }

    func resolve<T>(_ type: T.Type) -> T {
        dependencies.first(where: { $0 as? T != nil }) as! T
    }
}

MainResolver.shared.register(UserDefaults.standard)

@propertyWrapper
struct Inject<Value> {
    var wrappedValue: Value

    init(_ resolver: Resolver = MainResolver.shared) {
        wrappedValue = resolver.resolve(Value.self)
    }
}

class Service {
    @Inject var userDefaults: UserDefaults
}

let service = Service()
service.userDefaults.set("test", forKey: "key")
print(service.userDefaults.value(forKey: "key"))