title: Why can't I make an array of type NSLayoutConstraint?
body: <p>Basically, I am trying to reset some NSConstraints when the user taps a button.</p>
  
  <p><strong>My constraint outlets:</strong></p>
  
  <pre><code>@IBOutlet weak var firstButtonHeight: NSLayoutConstraint!
  @IBOutlet weak var secondButtonheight: NSLayoutConstraint!
  @IBOutlet weak var thirdButtonHeight: NSLayoutConstraint!
  </code></pre>
  
  <p><strong>Example action:</strong></p>
  
  <pre><code>@IBAction func firstButtonHeight(sender: UIButton) {
      firstButtonHeight.constant = 100
  }
  </code></pre>
  
  <p><br><br>
  I thought I could put them into an array (below) and iterate through them <em>before</em> running <code>firstButtonHeight.constant = 100</code>:</p>
  
  <pre><code>var constraints: [NSLayoutConstraint] = [firstButtonHeight, secondButtonheight, thirdButtonHeight]
  for constraint in constraints {
      constraint.constant = 50 //Original constraint value
  }
  </code></pre>
  
  <p>However, I get the error <code>Instance member 'firstButtonHeight' cannot be used on type 'ViewController'</code>. When did <code>firstButtonHeight</code> become a ViewController?</p>