Error compiling a custom container for boost spirit

Question

I want to parse something like the following:

1;2
=1200
3;4
5;6

lines can appear in any order. Lines starting with the = sign can be more than one and only the last one matters; lines containing a ; represent a pair of values that I want to store in a map. Reading the answer to this question I came up with some code that should be good enough (sorry but I'm still a noob with Spirit) and should do what I'm trying to achieve. Here's the code:

#define BOOST_SPIRIT_USE_PHOENIX_V3
#define DATAPAIR_PAIR

#include <iostream>
#include <boost/spirit/include/qi.hpp>
#include <boost/fusion/adapted/std_pair.hpp>
#include <boost/mpl/bool.hpp>
#include <map>
#if !defined(DATAPAIR_PAIR)
#include <vector>
#endif


static const char g_data[] = "1;2\n=1200\n3;4\n5;6\n";
typedef std::string DataTypeFirst;

#if defined(DATAPAIR_PAIR)
typedef std::string DataTypeSecond;
typedef std::pair<DataTypeFirst, DataTypeSecond> DataPair;
typedef std::map<DataTypeFirst, DataTypeSecond> DataMap;
#else
typedef std::vector<DataTypeFirst> DataPair;
typedef std::map<DataTypeFirst, DataTypeFirst> DataMap;
#endif

struct MyContainer {
    DataMap data;
    double number;
};

namespace boost { namespace spirit { namespace traits {
    template<> struct is_container<MyContainer> : boost::mpl::true_ {};

    template<>
    struct container_value<MyContainer> {
        typedef boost::variant<double, DataPair> type;
    };

    template <>
    struct push_back_container<MyContainer, double> {
        static bool call ( MyContainer& parContainer, double parValue ) {
            parContainer.number = parValue;
            return true;
        }
    };

    template <>
    struct push_back_container<MyContainer, DataPair> {
        static bool call ( MyContainer& parContainer, const DataPair& parValue ) {
#if defined(DATAPAIR_PAIR)
            parContainer.data[parValue.first] = parValue.second;
#else
            parContainer.data[parValue[0]] = parValue[1];
#endif
            return true;
        }
    };
} } }

template <typename Iterator>
struct TestGrammar : boost::spirit::qi::grammar<Iterator, MyContainer()> {

    TestGrammar ( void );
    boost::spirit::qi::rule<Iterator, MyContainer()> start;
    boost::spirit::qi::rule<Iterator, DataPair()> data;
    boost::spirit::qi::rule<Iterator, double()> num;
};

template <typename Iterator>
TestGrammar<Iterator>::TestGrammar() :
    TestGrammar::base_type(start)
{
    using boost::spirit::qi::alnum;
    using boost::spirit::qi::lit;
    using boost::spirit::ascii::char_;;
    using boost::spirit::qi::double_;
    using boost::spirit::qi::eol;
    using boost::spirit::qi::eoi;

    start %= *((num | data) >> (eol | eoi));
    data = +alnum >> lit(";") >> +alnum;
    num = '=' >> double_;
}

int main() {
    std::cout << "Parsing data:\n" << g_data << "\n";

    TestGrammar<const char*> gramm;
    MyContainer result;
    boost::spirit::qi::parse(static_cast<const char*>(g_data),
        g_data + sizeof(g_data) / sizeof(g_data[0]) - 1,
        gramm,
        result
    );
    std::cout << "Parsed data:\n";
    std::cout << "Result: " << result.number << "\n";
    for (const auto& p : result.data) {
        std::cout << p.first << " = " << p.second << '\n';
    }

    return 0;
}

I'm developing this on Gentoo Linux, using dev-libs/boost-1.55.0-r2:0/1.55.0 and gcc (Gentoo 4.8.3 p1.1, pie-0.5.9) 4.8.3. Compiling the above code I get an error like

/usr/include/boost/spirit/home/support/container.hpp:278:13: error: ‘struct MyContainer’ has no member named ‘insert’

as a workaround, I came up with the alternative code you get by commenting the "#define DATAPAIR_PAIR" line. In that case the code compiles and works, but what I really want is a pair where I can for example mix std::string and int values. Why using std::pair as the attribute for my data rule causes the compiler to miss the correct specialization of push_back_container? Is it possible to fix the code and have it working, either using std::pair or anything equivalent?

Answer 1

I'd simplify this by /just/ not treating things like a container and not-a-container at the same time. So for this particular situation I might deviate from my usual mantra (avoid semantic actions) and use them¹:

Live On Coliru

template <typename It, typename Skipper = qi::blank_type>
struct grammar : qi::grammar<It, MyContainer(), Skipper> {
    grammar() : grammar::base_type(start) {
        update_number = '=' > qi::double_ [ qi::_r1 = qi::_1 ];
        map_entry     = qi::int_ > ';' > qi::int_;

        auto number = phx::bind(&MyContainer::number, qi::_val);
        auto data   = phx::bind(&MyContainer::data, qi::_val);

        start         = *(
            (   update_number(number) 
              | map_entry [ phx::insert(data, phx::end(data), qi::_1) ]
            )
            >> qi::eol);
    }

  private:
    qi::rule<It, void(double&),       Skipper> update_number;
    qi::rule<It, MyContainer::Pair(), Skipper> map_entry;
    qi::rule<It, MyContainer(),       Skipper> start;
};

If you can afford a (0;0) entry in your map, you can even dispense with the grammar:

Live On Coliru

std::map<int, int> data;
double number;

bool ok = qi::phrase_parse(f, l, 
       *(
            (qi::omit['=' > qi::double_ [phx::ref(number)=qi::_1]] 
          | (qi::int_ > ';' > qi::int_)
        ) >> qi::eol)
        , qi::blank, data);

I can try to make your "advanced spirit" approach work too, but it might take a while :)

---

¹ _{I use auto for readability, but of course you don't need to use that; just repeat the subexpressions inline or use BOOST_AUTO. Note that this is not generically good advice for stateful parser expressions (see BOOST_SPIRIT_AUTO)}