*qi::string is compatible with both std::string (concatenation) and std::vector<std::string> (push_back) attributes

gistfile1.txt

#include <string>
#include <vector>

#include <boost/spirit/include/qi.hpp>
using string_it_t = std::string::const_iterator;

int main() {
    using namespace boost::spirit;
    using namespace boost::spirit::qi;


    rule<string_it_t, std::string()> r;
    rule<string_it_t, std::vector<std::string>()> r2;
    r = +qi::string("foo") ;
    r2 = +qi::string("foo") ;
    std::string testcase("foofoofoofoo");
    std::string result;
    auto beg = testcase.cbegin();
    parse(beg, testcase.cend(), r, result);
    std::cout << "result: " << result << "\n";
    std::vector<std::string> result2;
    beg = testcase.cbegin();
    parse(beg, testcase.cend(), r2, result2);
    std::cout << "result2:\n";
    for( auto const& s : result2 ) {
        std::cout << s << "\n";
    }
}