title: Accessing fileprivate and private variables in extension and another class using swift 4
body: <p>I have been going through the recent swift docs and working out on few examples in understanding private and fileprivate keywords in swift4. I am trying to access a fileprivate and private variable in an extension of the same class and another class subclassing the class but the output is unfruitful. I'm using in the following way</p>
  
  <pre><code>  class privateUsageExample: UIViewController {
      private var priVar = false
      fileprivate var fPriVar = false
    }
  
    // usage of extension in the same class
  
    extension privateUsageExample: UITextFieldDelegate {
  
       if priVar{ // do something} // error : expected declaration
       if fPriVar{ // do something} // error : expected declaration
  
       func randFunc(){ 
          self. fPriVar = true // accessible don't know the reason 
        }
    }
  
    // access of private and fileprivate variables in another class different file
  
    class anotherUsageInDiffSwiftFile: privateUsageExample {
  
     priVar = false // inaccessible (how to access it)
     fPriVar = true // inaccessible (how to access it)
  
   }
  </code></pre>
  
  <p>can you please help me out in accessing priVar (private) and fPriVar (fileprivate) variable in the extension of the same class in the same file and in another class subclassing the class in the different file. </p>