gistfile1.swift

func getText(preprocess: @escaping (String) -> String) {
    self.text = "Requesting..."
    NetworkHandler.getText { [weak self] (success, text, error)  in
      guard let self = self else { return }
      guard success, let text = text else {
        DispatchQueue.main.async {
          self.text = error ?? "Something went wrong."
        }
        return
      }
      
      DispatchQueue.global().async {
        let string = preprocess(text)
        
        DispatchQueue.main.async {
          self.text = string
        }
      }
    }
  }