Creating a vector of shared pointers by Spirit Qi

This is the next question from the previous question .

I can parse into vectors of strings from my grammar, but I cannot make out into a vector of common pointers to strings; those. std::vector<std::shared_ptr<std::string> >

and need a little help.

My compilation header:

#define BOOST_SPIRIT_USE_PHOENIX_V3 1


#include <boost/spirit/include/qi_core.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <iostream>
#include <string>


#include <boost/spirit/include/phoenix_stl.hpp>

#include <boost/phoenix/bind/bind_member_function.hpp>
#include <boost/spirit/include/phoenix_fusion.hpp>



// this solution for lazy make shared comes from the SO forum, user sehe.
// https://stackoverflow.com/questions/21516201/how-to-create-boost-phoenix-make-shared
//    post found using google search terms `phoenix construct shared_ptr`
// changed from boost::shared_ptr to std::shared_ptr
namespace {
    template <typename T>
    struct make_shared_f
    {
        template <typename... A> struct result
        { typedef std::shared_ptr<T> type; };

        template <typename... A>
        typename result<A...>::type operator()(A&&... a) const {
            return std::make_shared<T>(std::forward<A>(a)...);
        }
    };

    template <typename T>
    using make_shared_ = boost::phoenix::function<make_shared_f<T> >;
}




namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;


template<typename Iterator, typename Skipper = ascii::space_type>
struct SystemParser : qi::grammar<Iterator, std::vector<std::shared_ptr<std::string> >(), Skipper>
{


    SystemParser() : SystemParser::base_type(variable_group_)
    {
        namespace phx = boost::phoenix;
        using qi::_1;
        using qi::_val;
        using qi::eps;
        using qi::lit;


        var_counter = 0;

        declarative_symbols.add("variable_group",0);

        variable_group_ = "variable_group" > genericvargp_ > ';';
        genericvargp_ = new_variable_ % ','; //
        new_variable_ = unencountered_symbol_ [_val = make_shared_<std::string>() (_1)];
        unencountered_symbol_ = valid_variable_name_ - ( encountered_variables | declarative_symbols );
        valid_variable_name_ = +qi::alpha >> *(qi::alnum | qi::char_("[]_") );



//      debug(variable_group_); debug(unencountered_symbol_); debug(new_variable_); debug(genericvargp_);
//      BOOST_SPIRIT_DEBUG_NODES((variable_group_) (valid_variable_name_) (unencountered_symbol_) (new_variable_) (genericvargp_))
    }


    // rule declarations.  these are member variables for the parser.
    qi::rule<Iterator, std::vector<std::shared_ptr<std::string> >(), Skipper > variable_group_;
    qi::rule<Iterator, std::vector<std::shared_ptr<std::string> >(), Skipper > genericvargp_;
    qi::rule<Iterator, std::shared_ptr<std::string()> >  new_variable_;
    qi::rule<Iterator, std::string()> unencountered_symbol_;
    qi::rule<Iterator, std::string()> valid_variable_name_;


    unsigned var_counter;
    qi::symbols<char,int> encountered_variables;
    qi::symbols<char,int> declarative_symbols;
};

      

        
        
        
      

    

with driver code:

int main(int argc, char** argv)
{

    std::vector<std::shared_ptr<std::string> > V;
    std::string str = "variable_group x, y, z; ";


    std::string::const_iterator iter = str.begin();
    std::string::const_iterator end = str.end();


    SystemParser<std::string::const_iterator> S;


    bool s = phrase_parse(iter, end, S, boost::spirit::ascii::space, V);

    if (s)
    {
        std::cout << "Parse succeeded: " << V.size() << " variables\n";
        for (auto& s : V)
            std::cout << " - '" << s << "'\n";
    }
    else
        std::cout << "Parse failed\n";

    if (iter!=end)
        std::cout << "Remaining unparsed: '" << std::string(iter, end) << "'\n";


    return 0;
}

      

        
        
        
      

    

The text is parsed correctly, but the resulting vector has length 0, while the length should be 3. Somehow, it is std::shared_ptr<string>

not pressed on the back of the vector obtained from the rule genericvargp_

.

I've tried a lot of things, including reading all the debug information from test parsing and placing signs %=

for rule definitions to be used for rules for which there is a semantic action that doesn't assign _val

if I'm not mistaken. I also played all night and day using phx::bind

manual back push _val

but didn't get anywhere. I also confirmed that the make_shared_

one provided by sehe in another answer is actually lazy for std :: shared_ptr.

As an aside, I also struggled with getting the result unencountered_symbol_

to append to encountered_variables

to ensure that the variable names are unique ...

The problem is to propagate the result of the rule new_variable_

to the desired vector of shared pointers in the rule genericvargp_

.