title: Instance member 'decodeJson' cannot be used on type 'Utils'
body: <p>I confront a problem and i tried different solutions but i couldn't solve yet. The problem is <code>Instance member 'decodeJson' cannot be used on type 'Utils'</code> on <code>decodeJson</code> area. As you can see Utils class has different functions which <code>getDataWithURLSession</code>, <code>decodeJson</code> and <code>getDataWithURLSession</code> need to use <code>decodeJson</code>. </p>
  
  <pre><code>public class Utils {
  
      static var ApiURL = "http://xxx"
  
      var categoryList = [MangaCategory]()
  
      //MARK - JSON Searilization
      @available(iOS 10.0, *)
      static func getDataWithURLSession(withtoken: String){
          guard let url = URL(string: Utils.ApiURL + "/Category/Get") else {return}
          var request = URLRequest(url: url)
  
          request.httpMethod = "POST"
          request.addValue("application/json", forHTTPHeaderField: "Content-Type")
          request.setValue("Bearer " + withtoken, forHTTPHeaderField: "Authorization")
  
          guard let httpBody = try? JSONSerialization.data(withJSONObject: [], options: []) else { return }
          request.httpBody = httpBody
  
          let task = URLSession.shared.dataTask(with: request) { (data, response, err) in
  
              decodeJson(data: data)
          }
          task.resume()
      }
  
      @available(iOS 10.0, *)
      private func decodeJson(data:Data?){
          guard let data = data else {return}
          dump(data)
  
          do {
              let json = try JSONDecoder().decode(Categorys.self, from: data)
              for manga in json.data{
                  if json.data.count &gt; categoryList.count
                  {
                      let cat = MangaCategory(context: CoreDataService.context)
  
                      cat.category_name = manga.name
                      cat.category_id = Int16(manga.id)!
  
                      CoreDataService.saveContext()
                      self.categoryList.append(cat)
                  }
                  else{
                      print("JSon Serialization Es Geçildi.")
                  }
              }
  
          } catch let jsonError {
              print("JSON Serializing error : ", jsonError)
  
          }
      }
  }
  </code></pre>