Boost spirit x3 example calculator (calc8, calc9)

I'm very new with boost spirit (and with boost). Its very interesting library.

I use qtcreator + MinGW 5.3. I simply add every source file from git_hub_calc8 into new project and add some boost library, but i got the following error trying to build (All other examples work fine)

C:\Program Files\boost\boost\boost\spirit\home\x3\nonterminal\rule.hpp:113: ошибка: undefined reference to `bool client::parser::parse_rule<__gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, boost::spirit::x3::context<boost::spirit::x3::error_handler_tag, std::reference_wrapper<boost::spirit::x3::error_handler<__gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, boost::spirit::x3::context<boost::spirit::x3::skipper_tag, boost::spirit::x3::char_class<boost::spirit::char_encoding::ascii, boost::spirit::x3::space_tag> const, boost::spirit::x3::unused_type> >, std::__cxx11::list<client::ast::statement, std::allocator<client::ast::statement> > >(boost::spirit::x3::rule<client::parser::statement_class, std::__cxx11::list<client::ast::statement, std::allocator<client::ast::statement> >, false>, __gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&, __gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > const&, boost::spirit::x3::context<boost::spirit::x3::error_handler_tag, std::reference_wrapper<boost::spirit::x3::error_handler<__gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, boost::spirit::x3::context<boost::spirit::x3::skipper_tag, boost::spirit::x3::char_class<boost::spirit::char_encoding::ascii, boost::spirit::x3::space_tag> const, boost::spirit::x3::unused_type> > const&, std::__cxx11::list<client::ast::statement, std::allocator<client::ast::statement> >&)'

What did i wrong? How should i create project with this example?

Seems like a problem with BOOST_SPIRIT_DECLARE beacause a place pointed out by error is call for a template function connected with this define

(template <typename Iterator, typename Context, typename Attribute_>
        bool parse(Iterator& first, Iterator const& last
          , Context const& context, unused_type, Attribute_& attr) const
        {
            return parse_rule(*this, first, last, context, attr);
        }

The BOOST_SPIRIT_INSTANTIATE marco is equivalent to doing

namespace client { namespace parser
{

    template bool parse_rule<iterator_type, context_type, statement_type::attribute_type>(
        statement_type rule_, iterator_type &first, iterator_type const &last,
        context_type const &context,
        statement_type ::attribute_type &attr);
                                                                        ;
}}

So the crucial bit is that iterator_type and context_type match exactly the ones required at the call site. Now, the unresolved symbol is (demangled):

bool client::parser::parse_rule<
    __gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >,
    boost::spirit::x3::context<
        boost::spirit::x3::error_handler_tag,
        std::reference_wrapper<boost::spirit::x3::error_handler<__gnu_cxx::__normal_iterator<
            char const *, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >,
        boost::spirit::x3::context<
            boost::spirit::x3::skipper_tag,
            boost::spirit::x3::char_class<boost::spirit::char_encoding::ascii, boost::spirit::x3::space_tag> const,
            boost::spirit::x3::unused_type> >,
    std::__cxx11::list<client::ast::statement, std::allocator<client::ast::statement> >
>
(boost::spirit::x3::rule<client::parser::statement_class, std::__cxx11::list<client::ast::statement, std::allocator<client::ast::statement> >, false>,
__gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >&,
__gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > const&,
    boost::spirit::x3::context<
        boost::spirit::x3::error_handler_tag,
        std::reference_wrapper<boost::spirit::x3::error_handler<__gnu_cxx::__normal_iterator<
            char const *, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >,
        boost::spirit::x3::context<
            boost::spirit::x3::skipper_tag,
            boost::spirit::x3::char_class<boost::spirit::char_encoding::ascii, boost::spirit::x3::space_tag> const,
            boost::spirit::x3::unused_type> > const &,
std::__cxx11::list<client::ast::statement, std::allocator<client::ast::statement> >&)

This implies the iterator_type should be:

__gnu_cxx::__normal_iterator<char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >,

Which is indeed what std::string::const_iterator expands to on my system. So, the mismatch is likely in the context type. By adding a forced type error above the BOOST_SPIRIT_INSTANTIATE invocation like so:

struct {} _ = *static_cast<client::parser::context_type*>(nullptr);

I was able to force the compiler to output the expanded type of context_type at the point of instantiation:

statement.cpp:12 error: conversion from ‘client::parser::context_type {aka boost::spirit::x3::context<boost::spirit::x3::error_handler_tag, const std::reference_wrapper<boost::spirit::x3::error_handler<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> > > >, boost::spirit::x3::context<boost::spirit::x3::skipper_tag, const boost::spirit::x3::char_class<boost::spirit::char_encoding::ascii, boost::spirit::x3::space_tag>, boost::spirit::x3::unused_type> >}’ to non-scalar type ‘client::parser::<anonymous struct>’ requested

Which tells us the context type is (formatted for legibility):

boost::spirit::x3::context<
    boost::spirit::x3::error_handler_tag,
    const std::reference_wrapper<boost::spirit::x3::error_handler<
        __gnu_cxx::__normal_iterator<const char *, std::__cxx11::basic_string<char> > > >,
    boost::spirit::x3::context<
        boost::spirit::x3::skipper_tag,
        boost::spirit::x3::char_class<boost::spirit::char_encoding::ascii, boost::spirit::x3::space_tag> const,
        boost::spirit::x3::unused_type> >,

BUT: the linker has it as

boost::spirit::x3::context<
    boost::spirit::x3::error_handler_tag,
    std::reference_wrapper<boost::spirit::x3::error_handler<
        __gnu_cxx::__normal_iterator<const char *, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >,
    boost::spirit::x3::context<
        boost::spirit::x3::skipper_tag,
        boost::spirit::x3::char_class<boost::spirit::char_encoding::ascii, boost::spirit::x3::space_tag> const,
        boost::spirit::x3::unused_type> >

The most conspicuous difference is in the spelling of the defaulted template arguments on std::basic_string (char_traits and the allocator), but that's not actually a difference. The difference that DOES matter, though, is the absense of const with the reference_wrapper<> type.

Fixing It

I suppose this might have been a change once upon a time in the history of X3. The easiest fix in this case is to drop the const in config.hpp:

typedef x3::context<
    error_handler_tag
  , std::reference_wrapper<error_handler_type>
  , phrase_context_type>
context_type;

And indeed, it now compiles