Ticket #8529: stream_generator.cpp

//Purpose:
//  Demonstrate that a stream generator causes call to
/*
        // this is a special overload to detect if the output iterator has been
        // generated by a format_manip object.
        template <
            typename T, typename Traits, typename Properties, typename Context
          , typename Delimiter, typename Attribute
        >
        static bool generate(
            karma::detail::output_iterator<
                karma::ostream_iterator<T, Char, Traits>, Properties
            >& sink, Context& context, Delimiter const& d
          , Attribute const& attr)
        {

 */
 //  in boost/spirit/home/karma/stream/stream.hpp.
 //
//#include <boost/utility/demangled_type_name.hpp>
#include <boost/spirit/include/karma.hpp>

#include <sstream>
namespace client
{
    ///////////////////////////////////////////////////////////////////////////
    //  Use stream generator and list operator to 
    //  generator a Attribute.
    ///////////////////////////////////////////////////////////////////////////
    template <typename OutputIterator, typename Attribute>
    bool generate_by_stream(OutputIterator& sink, Attribute const& v)
    {
        using boost::spirit::karma::stream;
        using boost::spirit::karma::generate;

        bool r = generate(
            sink,    // destination: output iterator
            stream,  // the generator.  Should just use operator<< on v.
            v        // the attribute to output 
        );
        return r;
    }

}

////////////////////////////////////////////////////////////////////////////
//  Following(till Main program), is just to allow breakpoint to be
//  set in operator<< to allow using debugger to see how
//  karma implements the stream generator.
////////////////////////////////////////////////////////////////////////////
struct wrap_uns
{
    unsigned my_val;
    wrap_uns(unsigned a_val)
    : my_val(a_val)
    {}
};

namespace std
{
    //MAINTENANCE_NOTE:2013-04-09.Larry Evans:
    //  Must put following operator<< in std for
    //  ADL, as explained here:
    //
    //    http://boost.2283326.n4.nabble.com/karma-stream-generator-works-on-int-but-not-on-vector-lt-int-gt-tc4645053.html#a4645055
    //
    std::ostream&
    operator<< (std::ostream& os, wrap_uns const& z)
    {
        os<<"wrap_uns("<<z.my_val<<")";
        return os;
    }
}//exit namespace std

////////////////////////////////////////////////////////////////////////////
//  Main program
////////////////////////////////////////////////////////////////////////////
int
main()
{
    std::ostringstream ostream_sink;
      boost::spirit::karma::ostream_iterator
      < std::ostream::char_type
      >
    sink_iter(ostream_sink);
    wrap_uns attr(999);
    ostream_sink<<"***{generation.\n";
    bool const ok_gen=client::generate_by_stream(sink_iter, attr);
    ostream_sink<<"\n***}generation.\n";
    ostream_sink.flush();
    std::string generated=ostream_sink.str();
    if(!ok_gen)
    {
        std::cout << "-------------------------\n";
        std::cout << "Generating failed\n";
        std::cout << "-------------------------\n";
    }
    else
    {
        std::cout << "-------------------------\n";
        std::cout << "Generated:\n" << generated << "\n";
        std::cout << "-------------------------\n";
    }

    return 0;
}