title: Get return type of NSMethodSignature
body: <p>I need to check the return type of an <code>NSInvocation</code> to see if it is an object (from there I can use <code>isKindOfClass:</code> to check the exact kind of object). I see that <code>NSInvocation</code> has an <code>NSMethodSignature</code>, which in turn has <code>methodReturnType</code>. However, the documentation gives the following warning:</p>
  
  <blockquote>
    <p>This encoding is implementation-specific, so applications should use it with caution.</p>
  </blockquote>
  
  <p>So, how do I safely check if the return type is an object? Is there a decode variant of <code>@encode(type-name)</code>?</p>