title: NSUndoManager and GLKit
body: <p>I'm trying to support undo/redo in an iOS app that uses <a href="http://developer.apple.com/library/ios/documentation/GLkit/Reference/GLKit_Collection/_index.html" rel="nofollow">GLKit</a>.</p>
  
  <p>When I try the following:</p>
  
  <pre><code>GLKVector3 currentTranslation = _panningObject.translation;
  [[self.undoManager prepareWithInvocationTarget:_panningObject] setTranslation:currentTranslation];
  </code></pre>
  
  <p>I get a crash:</p>
  
  <pre><code>*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+[NSMethodSignature signatureWithObjCTypes:]: unsupported type encoding spec '(' in '4(_GLKVector3={?=fff}{?=fff}{?=fff}[3f])8''
  </code></pre>
  
  <p>Any ideas?</p>