     func fetchActivities(id: String, offset: String, limit: UInt, callback: ((UserServiceActivityListResult) -> Void)?)
     
     func editUserInfo(data: UserServiceInfoEditData, callback: ((UserServiceInfoEditResult) -> Void)?)
+    func changeAvatar(url: String, callback: ((UserServiceError?) -> Void)?)
 }
 
 struct UserServiceInfoEditData {

    case failedToFetchProfile(message: String)
    case failedToFetchActivities(message: String)
    case failedToEditUserInfo(message: String)
    
    var message: String {
        switch self {

             .failedToFetchFollowing(let message),
             .failedToFetchProfile(let message),
             .failedToFetchActivities(let message),
             .failedToEditUserInfo(let message),
             .failedToChangeAvatar(let message):
            return message
        }
    }
