title: Swift ios date as milliseconds Double or UInt64?
body: <p>I'm not iOS developer but started learning Swift.</p>
  
  <p>I try to convert some logic from Android project to iOS.</p>
  
  <p>I have the following method:</p>
  
  <pre><code>func addGroupItemSample(sample : WmGroupItemSample){ // some custom class
  
      var seconds: NSTimeInterval = NSDate().timeIntervalSince1970
      var  cuttDate:Double =  seconds*1000;
  
      var sampleDate: UInt64 = sample.getStartDate(); // &lt;-- problematic place
  
  if(sampleDate &gt; cuttDate){
     // ....
    }
  }
  </code></pre>
  
  <p>From the method above you can see that <code>sample.getStartDate()</code> returns type <code>UInt64</code>. </p>
  
  <p>I thought it's like <code>long</code> in Java: <code>System.currentTimeMillis()</code></p>
  
  <p>But current time in milliseconds defined as <code>Double</code>.</p>
  
  <p>Is it a proper way to mix <code>Double</code> and <code>UInt64</code> or do I need to represent all milliseconds as <code>Double</code> only?</p>
  
  <p>Thanks,</p>