title: Arguments by reference in Objective-C
body: <p>I'm trying to pass an <code>NSString</code> by reference but it doesn't work.</p>
  
  <p>This is the function:</p>
  
  <pre><code>+(void)fileName:(NSString *) file
  {
      file = @"folder_b";
  }
  </code></pre>
  
  <p>and this is the call:</p>
  
  <pre><code>NSString *file;
  
  [function fileName:file];
  
  nslog(@"%@",file);    // and there is nothing in the string....
  </code></pre>
  
  <p>What I must do to pass my string by reference?</p>