clang doesn't like boost::signals2?

Question

All day I kept on getting compiler errors from parts of code using the Boost::Signals2 library. I've reduced what I'm trying to do to a minimal example:

#include <boost/signals2.hpp>

int foo();

struct first_nonzero
{
    using result_type = int;

    template <typename It>
    result_type operator()(It first, It last) const
    {
    while(first != last)
    {
        if(*first != 0)
        {
            return *first;
        }
    }
    return 0;
    }
};

int foo()
{
    using signal = boost::signals2::signal<int (), first_nonzero>;
    signal s;
    return s();
}

When I try to compile this snippet with

clang -o foo.o -c foo.cpp -std=c++11 -Weverything -Wno-c++98-compat

I get a template deduction error seemingly coming from the signals library itself:

In file included from foo.cpp:1:
In file included from /usr/include/boost/signals2.hpp:19:
In file included from /usr/include/boost/signals2/signal.hpp:38:
In file included from /usr/include/boost/signals2/variadic_signal.hpp:21:
/usr/include/boost/signals2/detail/variadic_slot_invoker.hpp:84:23: error: no matching function for call to 'get'
      return func(std::get<indices>(args)...);
                  ^~~~~~~~~~~~~~~~~
/usr/include/boost/signals2/detail/variadic_slot_invoker.hpp:78:18: note: in instantiation of function template specialization 'boost::signals2::detail::call_with_tuple_args<int>::m_invoke<int,
      boost::function<int ()>, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type,
      boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type>' requested here
      return m_invoke(resolver, func, indices_type(), args);
             ^
/usr/include/boost/signals2/detail/variadic_slot_invoker.hpp:120:18: note: in instantiation of function template specialization 'boost::signals2::detail::call_with_tuple_args<int>::operator()<boost::function<int
      ()>, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type,
      boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type>' requested here
      return call_with_tuple_args<result_type>()(connectionBody->slot.slot_function(), _args);
             ^
/usr/include/boost/signals2/detail/variadic_slot_invoker.hpp:106:18: note: in instantiation of function template specialization 'boost::signals2::detail::variadic_slot_invoker<int,
      >::m_invoke<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int ()> >,
      boost::signals2::mutex> > >' requested here
      return m_invoke(connectionBody,
             ^
/usr/include/boost/signals2/detail/slot_call_iterator.hpp:82:35: note: in instantiation of function template specialization 'boost::signals2::detail::variadic_slot_invoker<int,
      >::operator()<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int ()> >,
      boost::signals2::mutex> > >' requested here
          cache->result.reset(cache->f(*iter));
                              ^
/usr/include/boost/iterator/iterator_facade.hpp:514:20: note: in instantiation of member function 'boost::signals2::detail::slot_call_iterator_t<boost::signals2::detail::variadic_slot_invoker<int, >,
      std::_List_iterator<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int
      ()> >, boost::signals2::mutex> > >, boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int ()>
      >, boost::signals2::mutex> >::dereference' requested here
      return f.dereference();
               ^
/usr/include/boost/iterator/iterator_facade.hpp:639:18: note: (skipping 1 context in backtrace; use -ftemplate-backtrace-limit=0 to see all)
      return iterator_core_access::dereference(this->derived());
             ^
foo.cpp:14:16: note: in instantiation of member function 'boost::iterator_facade<boost::signals2::detail::slot_call_iterator_t<boost::signals2::detail::variadic_slot_invoker<int, >,
      std::_List_iterator<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int
      ()> >, boost::signals2::mutex> > >, boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int ()>
      >, boost::signals2::mutex> >, int, boost::single_pass_traversal_tag, const int &, long>::operator*' requested here
        if(*first != 0)
           ^
/usr/include/boost/signals2/detail/result_type_wrapper.hpp:53:18: note: in instantiation of function template specialization
      'first_nonzero::operator()<boost::signals2::detail::slot_call_iterator_t<boost::signals2::detail::variadic_slot_invoker<int, >,
      std::_List_iterator<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int
      ()> >, boost::signals2::mutex> > >, boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int ()>
      >, boost::signals2::mutex> > >' requested here
      return combiner(first, last);
             ^
/usr/include/boost/signals2/detail/signal_template.hpp:241:18: note: in instantiation of function template specialization 'boost::signals2::detail::combiner_invoker<int>::operator()<first_nonzero,
      boost::signals2::detail::slot_call_iterator_t<boost::signals2::detail::variadic_slot_invoker<int, >,
      std::_List_iterator<boost::shared_ptr<boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int
      ()> >, boost::signals2::mutex> > >, boost::signals2::detail::connection_body<std::pair<boost::signals2::detail::slot_meta_group, boost::optional<int> >, boost::signals2::slot<int (), boost::function<int ()>
      >, boost::signals2::mutex> > >' requested here
      return detail::combiner_invoker<typename combiner_type::result_type>()
             ^
/usr/include/boost/signals2/detail/signal_template.hpp:695:16: note: in instantiation of member function 'boost::signals2::detail::signal_impl<int (), first_nonzero, int, std::less<int>, boost::function<int ()>,
      boost::function<int (const boost::signals2::connection &)>, boost::signals2::mutex>::operator()' requested here
    return (*_pimpl)(BOOST_SIGNALS2_SIGNATURE_ARG_NAMES(BOOST_SIGNALS2_NUM_ARGS));
           ^
foo.cpp:27:13: note: in instantiation of member function 'boost::signals2::signal<int (), first_nonzero, int, std::less<int>, boost::function<int ()>, boost::function<int (const boost::signals2::connection &)>,
      boost::signals2::mutex>::operator()' requested here
    return s();
        ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/utility:141:5: note: candidate template ignored: failed template argument deduction
    get(std::pair<_Tp1, _Tp2>& __in) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/utility:146:5: note: candidate template ignored: failed template argument deduction
    get(std::pair<_Tp1, _Tp2>&& __in) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/utility:151:5: note: candidate template ignored: failed template argument deduction
    get(const std::pair<_Tp1, _Tp2>& __in) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/array:267:5: note: candidate template ignored: failed template argument deduction
    get(array<_Tp, _Nm>& __arr) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/array:276:5: note: candidate template ignored: failed template argument deduction
    get(array<_Tp, _Nm>&& __arr) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/array:284:5: note: candidate template ignored: failed template argument deduction
    get(const array<_Tp, _Nm>& __arr) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/tuple:756:5: note: candidate template ignored: failed template argument deduction
    get(tuple<_Elements...>& __t) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/tuple:763:5: note: candidate template ignored: failed template argument deduction
    get(const tuple<_Elements...>& __t) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/tuple:770:5: note: candidate template ignored: failed template argument deduction
    get(tuple<_Elements...>&& __t) noexcept
    ^
1 error generated.

After some time I decided to give into the crazy idea of trying a different compiler, and to my surprise if I compile the same snippet with

g++ -o foo.o -c foo.cpp -std=c++11 -Wall -Wextra -pedantic

I have no errors. I am running Debian clang version 3.2-7ubuntu1 (tags/RELEASE_32/final) (based on LLVM 3.2) and g++ (Ubuntu/Linaro 4.8.1-10ubuntu9) 4.8.1; Boost libraries 1.54.

Due to project restrictions it's not possible for me to use a different compiler. Is there a way I can stick to clang and still use the boost::signals2 library?

[Works fine on coliru](http://coliru.stacked-crooked.com/a/51fcdc08d0fd1be4) — dyp, Mar 05 '14 at 20:37

score 0 · Answer 1 · answered May 24 '14 at 14:10

I know this is an old question but some notes on the topic could be useful to other readers.

Since the problem seems to regard using std::get to access elements of a std::tuple the simplest things to try is to define BOOST_NO_CXX11_HDR_TUPLE (Boost Macro Reference).

From boost/signals2/detail/variadic_slot_invoker.hpp:

#ifdef BOOST_NO_CXX11_HDR_TUPLE
#include <boost/tuple/tuple.hpp>
#define BOOST_SIGNALS2_TUPLE boost::tuple
#define BOOST_SIGNALS2_GET boost::get
#else
#include <tuple>
#define BOOST_SIGNALS2_TUPLE std::tuple
#define BOOST_SIGNALS2_GET std::get
#endif

this way Boost will use boost::tuple / boost::get instead of std::tuple / std::get. (but boost::tuple doesn't have variadic template support at present).

Of course this is just a workaround. You can gain some time to upgrade Clang (version 3.3 / 3.4 works fine).

clang doesn't like boost::signals2?

1 Answers1