Problem using 'shared_ptr<T>::operator impl-defined-type()'

With Borland 5.5.1, I'm not having any luck using a shared_ptr in a boolean context. The compiler complains that the 'if' condition below contains an "Illegal structure operation". Is this a known deficiency with my compiler? -Greg Hickman #include <boost/shared_ptr.hpp> int main(int argc, char* argv[]) { boost::shared_ptr<int> intp; if (intp) // error here ; return 0; }