Ticket #6374: boost_exception_tuple.cc

#include <boost/exception/all.hpp>
#include <boost/tuple/tuple.hpp>

typedef boost::error_info<struct tag_error_string, std::string> error_string_entry;
typedef boost::error_info<struct tag_error_int, int> error_int_entry;

struct exception : virtual std::exception, virtual boost::exception
{ };

#ifndef WORKAROUND

//I don't see why this code as is shouldn't just work
#define THROW_EXCEPTION( cnd__, ... ) if( !(cnd__) ) { \
        BOOST_THROW_EXCEPTION( exception() << boost::make_tuple( __VA_ARGS__ ) ); }

#else

//Instead I have to pathcup for the empty case, and surprisingly also the 1-length case
#define THROW_EXCEPTION( cnd__, ... ) if( !(cnd__) ) { \
        BOOST_THROW_EXCEPTION( error_with_tags( exception(), boost::make_tuple( __VA_ARGS__ ) ) ); }

        template<typename E, typename T,int CNT>
        struct error_with_tags_helper
        {
                E const & operator()( E const & x, T const & t )
                {
                        x << t;
                        return x;
                }
        };

        template<typename E, typename T>
        struct error_with_tags_helper<E,T,0>
        {
                E const & operator()( E const & x, T const & t )
                {
                        return x;
                }
        };

        template<typename E, typename T>
        struct error_with_tags_helper<E,T,1>
        {
                E const & operator()( E const & x, T const & t )
                {
                        return x << boost::get<0>(t);
                }
        };

        template<typename E, typename T>
        inline E const & error_with_tags( E const & x, T const & t )
        {
                error_with_tags_helper<E,T,boost::tuples::length<T>::value> et;
                return et(x,t);
        }

#endif

int main()
{
        //Okay
        THROW_EXCEPTION( true, error_string_entry( "hello" ), error_int_entry( 123 ) );

        //Fail -- zero parameters
        THROW_EXCEPTION( true );

        //Fail -- one parameter
        THROW_EXCEPTION( true, error_string_entry( "hello" ) );
}