title: String characters count compatability with iOS7
body: <p>Using Swift 2, for a project that supports iOS 7 and later.</p>
  
  <p>I am trying to find the count of characters in a String, by using <code>string.characters.count</code>. However in the <em>Quick Help Inspector</em>, it shows the availability as <strong>iOS (9.0 and later)</strong>.</p>
  
  <p>I have used this method on an iPad with iOS 8.4 installed on it and it did not give any errors, and gave me the correct length of the string.</p>
  
  <p>What would happen if I were to use it on a device with iOS 7 installed on it?</p>