#include <boost/mpl/assert.hpp>

template<typename T> struct not_defined : boost::mpl::false_ { }; 
template<typename T> T GetGlobal(char const *name) 
{ BOOST_MPL_ASSERT(( not_defined<T> )); }

int main() { GetGlobal<int>("hello"); }

In function 'T GetGlobal(const char*) [with T = int]':
t.cpp:8:   instantiated from here
Line 5: error: no matching function for call to 'assertion_failed(mpl_::failed************ not_defined<int>::************)'
compilation terminated due to -Wfatal-errors.