Compilation failure under clang-11 -stdlib=libc++ -std=c++20

[madmongo1]

Test program:

#include <boost/signals2.hpp>
int main()
{
}

clang-11 -stdlib=libc++ -std=c++20 test.cpp

I apprears that the code relies on the presence of std::allocator::difference_type etc [which were removed in c++20 ?]

Error output:

In file included from <source>:1:

In file included from /celibs/boost_1_74_0/boost/signals2.hpp:19:

In file included from /celibs/boost_1_74_0/boost/signals2/signal.hpp:22:

In file included from /celibs/boost_1_74_0/boost/signals2/connection.hpp:21:

/celibs/boost_1_74_0/boost/signals2/detail/auto_buffer.hpp:143:37: error: no type named 'size_type' in 'std::__1::allocator<boost::shared_ptr<void>>'

        typedef typename Allocator::size_type            size_type;

                ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~

/celibs/boost_1_74_0/boost/signals2/connection.hpp:53:61: note: in instantiation of template class 'boost::signals2::detail::auto_buffer<boost::shared_ptr<void>, boost::signals2::detail::store_n_objects<10>, boost::signals2::detail::default_grow_policy, std::__1::allocator<boost::shared_ptr<void>>>' requested here

        auto_buffer<shared_ptr<void>, store_n_objects<10> > garbage;

                                                            ^

In file included from <source>:1:

In file included from /celibs/boost_1_74_0/boost/signals2.hpp:19:

In file included from /celibs/boost_1_74_0/boost/signals2/signal.hpp:22:

In file included from /celibs/boost_1_74_0/boost/signals2/connection.hpp:21:

/celibs/boost_1_74_0/boost/signals2/detail/auto_buffer.hpp:144:37: error: no type named 'difference_type' in 'std::__1::allocator<boost::shared_ptr<void>>'

        typedef typename Allocator::difference_type      difference_type;

                ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~

/celibs/boost_1_74_0/boost/signals2/detail/auto_buffer.hpp:143:37: error: no type named 'size_type' in 'std::__1::allocator<boost::variant<boost::shared_ptr<void>, boost::signals2::detail::foreign_void_shared_ptr>>'

        typedef typename Allocator::size_type            size_type;

                ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~

/celibs/boost_1_74_0/boost/signals2/detail/slot_call_iterator.hpp:65:27: note: in instantiation of template class 'boost::signals2::detail::auto_buffer<boost::variant<boost::shared_ptr<void>, boost::signals2::detail::foreign_void_shared_ptr>, boost::signals2::detail::store_n_objects<10>, boost::signals2::detail::default_grow_policy, std::__1::allocator<boost::variant<boost::shared_ptr<void>, boost::signals2::detail::foreign_void_shared_ptr>>>' requested here

        tracked_ptrs_type tracked_ptrs;

                          ^

In file included from <source>:1:

In file included from /celibs/boost_1_74_0/boost/signals2.hpp:19:

In file included from /celibs/boost_1_74_0/boost/signals2/signal.hpp:22:

In file included from /celibs/boost_1_74_0/boost/signals2/connection.hpp:21:

/celibs/boost_1_74_0/boost/signals2/detail/auto_buffer.hpp:144:37: error: no type named 'difference_type' in 'std::__1::allocator<boost::variant<boost::shared_ptr<void>, boost::signals2::detail::foreign_void_shared_ptr>>'

        typedef typename Allocator::difference_type      difference_type;

                ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~

4 errors generated.

Compiler returned: 1

Godbolt link: https://godbolt.org/z/cenzv1

$ clang++ --version
clang version 11.0.0 (Fedora 11.0.0-1.fc33)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

[glenfe]

Resolved in #47