PostsDataProvider.swift

struct PostsDataProviderA: DataProvider {

  let networkService: NetworkingA
  let userService: UserService

  func fetchPosts(withURL url: URL, completion: @escaping (Result<[Post], Error>) -> Void) {
    networkService.loadJSON(withURL: url, type: [Post].self, completion: completion)
  }
    
  func fetchUser(withId id: Int, completion: @escaping (User?) -> Void) {
    userService.getUser(withId: id, completion: completion)
  }
}


struct PostsDataProviderB: DataProvider {

  let networkService: NetworkingB
  let userService: UserService

  func fetchPosts(withURL url: URL, completion: @escaping (Result<[Post], Error>) -> Void) {
    networkService.load(url, type: [Post].self, completion: completion)
  }
    
  func fetchUser(withId id: Int, completion: @escaping (User?) -> Void) {
    userService.getUser(withId: id, completion: completion)
  }
}