#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/variant.hpp>

#include <iostream>
#include <string>

class Value
{
public:

    enum ValueType
    {
        BoolType,
        NumericType
    };

    Value(bool b) : type_(BoolType), value_(b) {}
    Value(const double d) : type_(NumericType), value_(d) {};

    ValueType type() { return type_; }

    operator bool() { return boost::get<bool>(value_); }
    operator double() { return boost::get<double>(value_); }

private:
    ValueType type_;
    boost::variant<bool, double> value_;

};

namespace karma = boost::spirit::karma;

int main()
{
    using karma::bool_;
    using karma::double_;
    using karma::rule;
    using karma::eps;

    std::string generated;
    std::back_insert_iterator<std::string> sink(generated);

    rule<std::back_insert_iterator<std::string>, Value()> value_rule = bool_ | double_;
    // rule<std::back_insert_iterator<std::string>, Value()> value_rule = (eps( ... ) << bool_) | (eps( ... ) << double_);

    Value bool_value = Value(true);
    Value double_value = Value(5.0);

    karma::generate(sink, value_rule, bool_value);
    std::cout << generated << "\n";

    generated.clear();

    karma::generate(sink, value_rule, double_value);
    std::cout << generated << "\n";

    return 0;
}