On 20 Aug 2009, at 23:57, Scott McMurray wrote:
2009/8/20 Edward Grace <ej.grace@imperial.ac.uk>:
if O is compatible with the concept of a functor and O returns a type that can be converted to a float, then we are good to go -- otherwise I'd like an intelligible error.
If, for example, O is of the type 'void (*)()' I'd like it (the compiler) to spit out, "The function pointer of type O must of signature float (*)()"
Sounds like you want something like the MPL_ASSERT example at [1] along with the result_of metafunction[2].
I'm starting to wonder if there's a problem with BOOST_MPL_ASSERT in g ++, as I understand it (this is quite probably the real problem....) the following minimal example should work #include <boost/mpl/assert.hpp> int main() { BOOST_MPL_ASSERT(( boost::is_same<unsigned,unsigned> )); // Should be ok! return 0; } When compiling, /sw/bin/g++-4 -I/usr/local/include -ansi -pedantic -Wall test.cpp test.cpp: In function 'int main()': test.cpp:4: error: expected primary-expression before 'enum' test.cpp:4: error: expected ';' before 'enum' Pre-processing (and smartening up for presentation) we get, int main() { static __const std::size_t mpl_assertion_in_line_4 = sizeof( boost::mpl::assertion_failed<false>( boost::mpl::assert_arg( (void (*) ( boost::is_same<unsigned,unsigned> ))0, 1 ) // <--- ))0,1 ) ???? ) ) ; // Should be ok! return 0; } -ed