MyCacheDelegate.swift

private func cacheError(message: String) -> NSError {
  return NSError(
    domain: "",
    code: 0,
    userInfo: [NSLocalizedDescriptionKey: message]
  )
}

class MyCacheDelegate: CacheDelegate {
  private var modelCache: [String: SimpleModel] = [:]
  private var collectionCache: [String: [SimpleModel]] = [:]

  func modelForKey<T : SimpleModel>(cacheKey: String?, context: Any?, completion: (T?, NSError?) -> ()) {
    guard let cacheKey = cacheKey else {
      return completion(.None, cacheError("cacheKey argument required"))
    }
    guard let model = modelCache[cacheKey] as? T else {
      return completion(.None, cacheError(
        "Object '\(String(T))' not found for key '\(cacheKey)'"
        ))
    }
    completion(model, .None)
  }

  func setModel<T: SimpleModel>(model: T, forKey cacheKey: String, context: Any?) {
    modelCache[cacheKey] = model
  }

  func collectionForKey<T: SimpleModel>(cacheKey: String?, context: Any?, completion: ([T]?, NSError?) -> ()) {
    guard let cacheKey = cacheKey else {
      return completion(.None, cacheError("cacheKey argument required"))
    }
    guard let model = collectionCache[cacheKey] as? [T] else {
      return completion(.None, cacheError(
        "Object '\(String(T))' not found for key '\(cacheKey)'"
        ))
    }
    completion(model, .None)
  }

  func setCollection<T: SimpleModel>(collection: [T], forKey cacheKey: String, context: Any?) {
    collectionCache[cacheKey] = collection.map { $0 as SimpleModel }
  }

  func deleteModel(model: SimpleModel, forKey cacheKey: String?, context: Any?) {
    guard let cacheKey = cacheKey else { return }
    modelCache.removeValueForKey(cacheKey)
    collectionCache.removeValueForKey(cacheKey)
  }
}