title: swift check if NSDate is nil without let
body: <p>I find very messy to use let to verify if a variable is nil or had been set a value previously.</p>
  
  <pre><code>var birthDate: NSDate?
  </code></pre>
  
  <p>There is a form where user can set their birthdate and this variable is assigned a value.</p>
  
  <p>Later in the doSave method I want to verify if this field was filled</p>
  
  <pre><code>@IBAction func doSave(sender: AnyObject) {
  ...
  if birthDate == nil {
      doAlert("You need to specify your birth date")
  } else { ... continue save ... }
  </code></pre>
  
  <p>The best approach I had obtained is to create a second variable, based on <a href="https://stackoverflow.com/questions/28140895/swift-check-nsdate-is-not-nil">another related question</a></p>
  
  <pre><code>if let bd = birthDate! as? NSDate { ... continue save ... }
  else { doAlert("You need to specify your birth date") }
  </code></pre>
  
  <p>I only get a warning: Conditional cast from 'NSDate' to 'NSDate' always succeeds</p>
  
  <p>Is this the only way to achieve this. Is there anything less messy?</p>