let defaults = Defaults() // or Defaults.shared

// Define a key
let key = Key<String>("someKey")
// Set a value
defaults.set("Codable FTW 😃", for: key)
// Read the value back
defaults.get(for: key) // Output: Codable FTW 😃

if defaults.has(key) {
    // Do your thing
}

// Extend with a custom key
extension DefaultsKey {
    static var someKey: Key<Int> { Key("someKey") }
}
// Then use it like this
defaults.set("Some key", for: .someKey)
defaults.get(for: .someKey) // Output: Some key

struct Person: Codable {
    let name: String
    let age: Int
}

// Create a key
let key = Key<Person>("personKey")
// Get an instance of your Codable conforming enum, struct or class
let person = Person(name: "Bonnie Greenwell", age: 80)
// Set the value
defaults.set(person, for: key)

// Read it back
let person = defaults.get(for: key)
person?.name // Bonnie Greenwell
person?.age  // 80

enum Pet: String, Codable {
    case cat
    case dog
}
struct Person: Codable {
    let name: String
    let pets: [Pet]
}
// Get a Codable conforming instante
let person = Person(name: "Claire", pets: [.cat])
// Set the value
defaults.set(person, for: key)
// And read it back
let person = defaults.get(for: key)
person?.name        // Claire
person?.pets.first  // cat