BOOST_FUSION_ADAPT_ADT explodes when using with boost::karma

Question

I'm not sure if this is related to Error when adapting a class with BOOST_FUSION_ADAPT_ADT ,but even if it is, the question behind it is still not answered/still fails see the comment of the author Error when adapting a class with BOOST_FUSION_ADAPT_ADT . (I used boost 1.69)

I have a struct

#include <string>
#include <cstdint>
namespace rtsp {
    struct request {
    };
    struct response {
        uint_fast16_t rtsp_version_major;
        uint_fast16_t rtsp_version_minor;
        uint_fast16_t status_code;
        std::string reason_phrase;
    };
    using message = boost::variant<request, response>;
}

Which I was able to use with boost::spirit::qi via

BOOST_FUSION_ADAPT_STRUCT(
        rtsp::response,
        (uint_fast16_t, rtsp_version_major)
        (uint_fast16_t, rtsp_version_minor)
        (uint_fast16_t, status_code)
        (std::string, reason_phrase)

but since I now also want to generate and not only parse the struct it, using boost::spirit::karma I have to use

BOOST_FUSION_ADAPT_ADT(
        rtsp::response,
(uint_fast16_t,const uint_fast16_t&,obj.rtsp_version_major, obj.rtsp_version_major = val)
(uint_fast16_t,const uint_fast16_t&,obj.rtsp_version_minor, obj.rtsp_version_minor = val)
(uint_fast16_t,const uint_fast16_t&,obj.status_code, obj.status_code = val)
(std::string,const std::string&,obj.reason_phrase, obj.reason_phrase = val)
)

But it explodes with several errors, from template errors up to syntax errors, for example with

In file included from /Users/markus/Entwicklung/HTW/RTSP-Streaming/src/streaming_lib/include/rtsp_request.hpp:11: In file included from /Users/markus/include/boost/spirit/include/qi.hpp:16: In file included from /Users/markus/include/boost/spirit/home/qi.hpp:14: In file included from /Users/markus/include/boost/spirit/home/qi/action.hpp:14: In file included from /Users/markus/include/boost/spirit/home/qi/action/action.hpp:16: /Users/markus/include/boost/spirit/home/qi/detail/attributes.hpp:153:9: error: ambiguous partial specializations of 'transform_attribute, unsigned short, boost::spirit::qi::domain, void>' : transform_attribute

Since it already fails at the #include <boost/spirit/include/qi.hpp> line, maybe someone knows how to correct the BOOST_FUSION_ADAPT_ADT phrase?

Whole code: /*! @file rtsp_request.hpp * */

#ifndef RTSP_GUI_RTSP_PARSER_HPP
#define RTSP_GUI_RTSP_PARSER_HPP

#include <string>
#include <cstdint>

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/fusion/include/adapt_adt.hpp>
#include <boost/fusion/adapted/adt/adapt_adt.hpp>
#include <boost/spirit/include/support_adapt_adt_attributes.hpp>



namespace rtsp {
    struct request {
    };
    struct response {
        uint_fast16_t rtsp_version_major;
        uint_fast16_t rtsp_version_minor;
        uint_fast16_t status_code;
        std::string reason_phrase;
    };
    using message = boost::variant<request, response>;
}
BOOST_FUSION_ADAPT_ADT(
        rtsp::response,
(uint_fast16_t,const uint_fast16_t&,obj.rtsp_version_major, obj.rtsp_version_major = val)
(uint_fast16_t,const uint_fast16_t&,obj.rtsp_version_minor, obj.rtsp_version_minor = val)
(uint_fast16_t,const uint_fast16_t&,obj.status_code, obj.status_code = val)
(std::string,const std::string&,obj.reason_phrase, obj.reason_phrase = val)
)
/*
BOOST_FUSION_ADAPT_STRUCT(
        rtsp::response,
        (uint_fast16_t, rtsp_version_major)
        (uint_fast16_t, rtsp_version_minor)
        (uint_fast16_t, status_code)
        (std::string, reason_phrase)
)*/
namespace rtsp {

    template<typename Iterator>
    struct rtsp_response_grammar
            : ::boost::spirit::qi::grammar<Iterator, response()> {
        rtsp_response_grammar() : rtsp_response_grammar::base_type(start) {
            namespace ns = ::boost::spirit::standard;
            using ::boost::spirit::qi::uint_parser;
            using ::boost::spirit::qi::lexeme;
            using ::boost::spirit::qi::lit;
            using boost::spirit::qi::omit;
            using ::boost::spirit::qi::repeat;
            quoted_string %= lexeme['"' >> +(ns::char_ - '"') >> '"'];
            status_code = uint_parser<uint_fast16_t, 10, 3, 3>();
            at_least_one_digit = uint_parser<uint_fast16_t, 10, 1>();

            start %= lit("RTSP/") >> at_least_one_digit >> "." >> at_least_one_digit >> omit[+ns::space]
                    >> status_code >> omit[+ns::space]
                    >> *(ns::char_ - (lit("\r") | lit("\n")))
                    >> lit("\r\n");
        }

        boost::spirit::qi::rule<Iterator, std::string()> quoted_string;
        boost::spirit::qi::rule<Iterator, uint_fast16_t()> status_code;
        boost::spirit::qi::rule<Iterator, uint_fast16_t()> at_least_one_digit;
        boost::spirit::qi::rule<Iterator, response()> start;

    };

    template <typename OutputIterator>
    bool generate_response(OutputIterator sink, const response& reponse)
    {
        using ::boost::spirit::karma::lit;

        return boost::spirit::karma::generate(sink, lit("RTSP/"), reponse);
    }
}


#endif //RTSP_GUI_RTSP_PARSER_HPP
/*! @file rtsp_request.cpp
 *
 */

#include "rtsp_request.hpp"

#include <iterator>

template
struct rtsp::rtsp_response_grammar<std::string::const_iterator>;

template
bool rtsp::generate_response<std::back_insert_iterator<std::string>>(std::back_insert_iterator<std::string> sink, const response& reponse);

BTW, trying to just use the BOOST_FUSION_ADAPT_STRUCT with the karma generator function would also fail with:

In file included from /Users/markus/Entwicklung/HTW/RTSP-Streaming/src/streaming_lib/src/rtsp_request.cpp:5: In file included from /Users/markus/Entwicklung/HTW/RTSP-Streaming/src/streaming_lib/include/rtsp_request.hpp:11: In file included from /Users/markus/include/boost/spirit/include/qi.hpp:16: In file included from /Users/markus/include/boost/spirit/home/qi.hpp:14: In file included from /Users/markus/include/boost/spirit/home/qi/action.hpp:14: In file included from /Users/markus/include/boost/spirit/home/qi/action/action.hpp:14: In file included from /Users/markus/include/boost/spirit/home/qi/meta_compiler.hpp:15: In file included from /Users/markus/include/boost/spirit/home/qi/domain.hpp:18: In file included from /Users/markus/include/boost/spirit/home/support/context.hpp:18: In file included from /Users/markus/include/boost/spirit/home/support/nonterminal/expand_arg.hpp:20: /Users/markus/include/boost/spirit/home/support/string_traits.hpp:156:26: error: implicit instantiation of undefined template 'boost::spirit::traits::char_type_of' typedef typename char_type_of::type char_type; ^ /Users/markus/include/boost/spirit/home/support/string_traits.hpp:242:14: note: in instantiation of template class 'boost::spirit::traits::extract_c_string' requested here typename extract_c_string::char_type const* ^ /Users/markus/include/boost/spirit/home/karma/string/lit.hpp:180:21: note: while substituting deduced template arguments into function template 'get_c_string' [with String = rtsp::response] get_c_string( ^ /Users/markus/include/boost/spirit/home/karma/generate.hpp:69:45: note: in instantiation of function template specialization 'boost::spirit::karma::literal_string::generate

, mpl_::int_<0>, boost::spirit::unused_type>, boost::spirit::context, boost::spirit::locals >, boost::spirit::unused_type, rtsp::response>' requested here return compile(expr).generate(sink, context, unused, attr); ^ /Users/markus/include/boost/spirit/home/karma/generate.hpp:91:23: note: in instantiation of function template specialization 'boost::spirit::karma::generate , mpl_::int_<0>, boost::proto::exprns_::expr > >, 0>, rtsp::response>' requested here return karma::generate(sink, expr, attr); ^ /Users/markus/Entwicklung/HTW/RTSP-Streaming/src/streaming_lib/include/rtsp_request.hpp:69:38: note: in instantiation of function template specialization 'boost::spirit::karma::generate , boost::proto::exprns_::expr > >, 0>, rtsp::response>' requested here return boost::spirit::karma::generate(sink, lit("RTSP/"), reponse); ^ /Users/markus/include/boost/spirit/home/support/string_traits.hpp:96:12: note: template is declared here struct char_type_of; ^ /Users/markus/include/boost/spirit/home/support/string_traits.hpp:179:20: error: no matching function for call to 'call' return extract_c_string::call(str); ^~~~~~~~~~~~~~~~~~~~~~~~~ /Users/markus/include/boost/spirit/home/support/string_traits.hpp:238:42: note: in instantiation of member function 'boost::spirit::traits::extract_c_string::call' requested here return extract_c_string::call(str); ^ /Users/markus/include/boost/spirit/home/karma/string/lit.hpp:180:21: note: in instantiation of function template specialization 'boost::spirit::traits::get_c_string' requested here get_c_string( ^ /Users/markus/include/boost/spirit/home/karma/generate.hpp:69:45: note: in instantiation of function template specialization 'boost::spirit::karma::literal_string::generate , mpl_::int_<0>, boost::spirit::unused_type>, boost::spirit::context, boost::spirit::locals >, boost::spirit::unused_type, rtsp::response>' requested here return compile(expr).generate(sink, context, unused, attr); ^ /Users/markus/include/boost/spirit/home/karma/generate.hpp:91:23: note: in instantiation of function template specialization 'boost::spirit::karma::generate , mpl_::int_<0>, boost::proto::exprns_::expr > >, 0>, rtsp::response>' requested here return karma::generate(sink, expr, attr); ^ /Users/markus/Entwicklung/HTW/RTSP-Streaming/src/streaming_lib/include/rtsp_request.hpp:69:38: note: in instantiation of function template specialization 'boost::spirit::karma::generate , boost::proto::exprns_::expr > >, 0>, rtsp::response>' requested here return boost::spirit::karma::generate(sink, lit("RTSP/"), reponse); ^ /Users/markus/include/boost/spirit/home/support/string_traits.hpp:159:25: note: candidate template ignored: could not match 'T ' against 'rtsp::response' static T const call (T* str) ^ /Users/markus/include/boost/spirit/home/support/string_traits.hpp:165:25: note: candidate template ignored: could not match 'const T ' against 'rtsp::response' static T const call (T const* str)

ADAPT_ADT has a rather broad tendency to explode. The proxies it uses are a leaky abstraction and they can easily trigger UB when used in "surprising" contexts. — sehe
So your pragmatic advise is to not use the fusion abstraction in karma until, spirit manages to get loose from fusion? — Superlokkus
@NikitaKniazev I can't since it also generates errors, when instantiating the karma generator function rtsp::generate_response with a back_inserter iterator for a std::string: ... /Users/markus/include/boost/spirit/home/support/string_traits.hpp:156:26: error: implicit instantiation of undefined template 'boost::spirit::traits::char_type_of<rtsp::response>' typedef typename char_type_of<String>::type char_type; — Superlokkus
@NikitaKniazev fair enough. I'll still give that recommendation even if I'm absolutely sure all bugs have gone. And that's just because of professional experience: one rarely needs the complexity and it's avoidable. (Like I hinted before, I find that "requiring" ADT adaptation is frequently a code smell of too much responsibility on 1 class - mixing levels of abstraction viewed another way. Of course, it might be desired for an optimization, but I'd rarely suggest rolling a Qi parser in such cases). Cheers! — sehe

Nikita Kniazev Nikita Kniazev · Accepted Answer · 2018-09-07T15:43:41

A well defined grammar handles either BOOST_FUSION_ADAPT_STRUCT or BOOST_FUSION_ADAPT_ADT without problems.

Example:

namespace rtsp {
    ...

    template <typename OutputIterator>
    bool generate_response(OutputIterator sink, const response& reponse)
    {
        using ::boost::spirit::karma::lit;
        using ::boost::spirit::karma::uint_;
        using ::boost::spirit::karma::string;

        return boost::spirit::karma::generate(sink,
            lit("RTSP/") << uint_ << "." << uint_ << " " << uint_ << " " << string
          , reponse);
    }
}

int main()
{
    std::string s;
    generate_response(std::back_inserter(s), rtsp::response{ 1, 0, 200, "OK" });
    std::cout << s;
}

Prints: RTSP/1.0 200 OK

Update: Qi bug involving BOOST_FUSION_ADAPT_ADT confirmed and reported.

BOOST_FUSION_ADAPT_ADT explodes when using with boost::karma

1 Answers