title: How to declare keyword variable in Swift
body: <p>I am a new iOS programming. I am creating a sample app which get data and set data using Firestore. For the collection contains some documents which and named those properties like <code>extension</code>... So in programming I need to create variable with that name <code>extension</code> in order to set data to Firestore but Xcode is warning me that I don't have to declare that variable name. </p>
  
  <p>I have been trying to figure it out but not work. So, I decided to ask my own question if there any technique to delacre variable name which is warning by Xcode.</p>