title: How is the itk::SmartPointer converted to bool?
body: <p>The <a href="http://www.itk.org/Doxygen/html/itkSmartPointer_8h_source.html" rel="nofollow">smart pointer used by the ITK library</a> can be implicitly converted to <code>bool</code>, for example in an <code>if</code> clause. It's very convenient, but I'd like to make sure how it works. My guess is that C++ uses the provided <code>operator==</code> to compare to 0, but I couldn't find any documentation describing this behavior. Is this really what's happening?
  <a href="http://www.itk.org/Doxygen/html/classitk_1_1SmartPointer.html" rel="nofollow">Here</a> is the Doxygen page for the class, for people who might find it more convenient than the code itself.</p>