title: How to get the unwrapped type from an optional type in Swift?
body: <p>I'm trying to get an unwrapped type from an optional type in runtime.
  The following code would print the type of a as <code>Optional&lt;String&gt;</code>. </p>
  
  <pre><code>class MySubClass: MyClass {
  
      var a: String? = nil
  }
  
  var a = MySubClass()
  
  let mirror = Mirror(reflecting: a)
  for child in mirror.children {
      print(child.value.dynamicType)
  }
  </code></pre>
  
  <p>Now I want to unwrap the type and get <code>String</code>, what should I do to make this happen in runtime? </p>