onmyway133

public class Transformer<T> {
  let toData: (T) throws -> Data
  let fromData: (Data) throws -> T

  public init(toData: @escaping (T) throws -> Data, fromData: @escaping (Data) throws -> T) {
    self.toData = toData
    self.fromData = fromData
  }
}

onmyway133

/// A protocol used for saving and loading from storage
public protocol StorageAware {
  associatedtype T
  
  ...
}

onmyway133

let storage: Storage<User> = ...
storage.setObject(superman, forKey: "user")

let imageStorage = storage.transformImage() // Storage<UIImage>
imageStorage.setObject(image, forKey: "image")

let stringStorage = storage.transformCodable(ofType: String.self) // Storage<String>
stringStorage.setObject("hello world", forKey: "string")

onmyway133

class DataProducer<T: Codable> {
  let object: T?
  let image: Image?

  init(object: T) {
    self.object = object
    self.image = nil
  }

  init(image: Image) {

onmyway133

protocol DataConvertible {
  func toData() -> Data
  static func fromData() -> Self
}

// WARNING: Does not compile
extension Codable: DataConvertible { // Non-nominal type 'Codable' (aka 'Decodable & Encodable') cannot be extended

}

onmyway133

// WARNING: Does not compile
extension Storage {
  func save(object: Any, forKey: String) {
    switch object {
    case let image as Image:
      let data = UIImagePNGRepresentation(image)
    case let object as Codable:
      let encoder = JSONEncoder()
      try? encoder.encode(object) // Cannot invoke 'encode' with an argument list of type '(Codable)'
    default:

onmyway133

extension TypeWrapperStorage: StorageAware {
  public func entry<T: Codable>(forKey key: String) throws -> Entry<T> {
    let wrapperEntry = try internalStorage.entry(forKey: key) as Entry<TypeWrapper<T>>
    return Entry(object: wrapperEntry.object.object, expiry: wrapperEntry.expiry)
  }
 
  public func setObject<T: Codable>(_ object: T, forKey key: String,
                                    expiry: Expiry? = nil) throws {
    let wrapper = TypeWrapper<T>(object: object)
    try internalStorage.setObject(wrapper, forKey: key, expiry: expiry)

onmyway133

struct PrimitiveWrapper<T: Codable>: Codable {
  let value: T
 
  init(value: T) {
    self.value = value
  }
}

onmyway133

extension PrimitiveStorage: StorageAware {
  public func entry<T: Codable>(forKey key: String) throws -> Entry<T> {
    do {
      return try internalStorage.entry(forKey: key) as Entry<T>
    } catch let error as Swift.DecodingError {
      // Expected to decode T but found a dictionary instead.
      switch error {
      case .typeMismatch(_, let context) where context.codingPath.isEmpty:
        let wrapperEntry = try internalStorage.entry(forKey: key) as Entry<PrimitiveWrapper<T>>
        let primitiveEntry = Entry(object: wrapperEntry.object.value,

onmyway133

let wrapper = ImageWrapper(image: starIconImage)
try? storage.setObject(wrapper, forKey: "star")

let icon = try? storage.object(ofType: ImageWrapper.self, forKey: "star").image