boost::bind with explicit result type and noexcept under C++17 fails

[Dani-Hub]

When compiling the following code requiring C++17 (or higher) with any recent compiler that has made exception specification part of the function type (Clang 12, gcc 11, VC 2019),

#include <boost/type.hpp> 
#include <boost/bind/bind.hpp>

struct P
{
  P() 
  {
    boost::bind(boost::type<void>(), &P::launch_me, this)();
  }  

  void launch_me() noexcept {}
};

the build fails, e.g. as follows:

In file included from prog.cc:2:
In file included from /opt/wandbox/boost-1.73.0/clang-head/include/boost/bind/bind.hpp:26:
In file included from /opt/wandbox/boost-1.73.0/clang-head/include/boost/mem_fn.hpp:22:
/opt/wandbox/boost-1.73.0/clang-head/include/boost/bind/mem_fn.hpp:356:16: error: reference to non-static member function must be called; did you mean to call it with no arguments?
        return (p->*f_);
               ^~~~~~~~
                       ()
/opt/wandbox/boost-1.73.0/clang-head/include/boost/bind/bind.hpp:259:9: note: in instantiation of member function 'boost::_mfi::dm<void () noexcept, P>::operator()' requested here
        unwrapper<F>::unwrap(f, 0)(a[base_type::a1_]);
        ^
/opt/wandbox/boost-1.73.0/clang-head/include/boost/bind/bind.hpp:1294:16: note: in instantiation of function template specialization 'boost::_bi::list1<boost::_bi::value<P *>>::operator()<void (P::*)() noexcept, boost::_bi::list0>' requested here
        return l_( type<result_type>(), f_, a, 0 );
               ^
prog.cc:8:58: note: in instantiation of member function 'boost::_bi::bind_t<void, void (P::*)() noexcept, boost::_bi::list1<boost::_bi::value<P *>>>::operator()' requested here
    boost::bind(boost::type<void>(), &P::launch_me, this)();
                                                         ^
In file included from prog.cc:2:
In file included from /opt/wandbox/boost-1.73.0/clang-head/include/boost/bind/bind.hpp:26:
In file included from /opt/wandbox/boost-1.73.0/clang-head/include/boost/mem_fn.hpp:22:
/opt/wandbox/boost-1.73.0/clang-head/include/boost/bind/mem_fn.hpp:356:16: error: non-const lvalue reference to type 'void () noexcept' cannot bind to a temporary of type 'void'
        return (p->*f_);
               ^~~~~~~~~
2 errors generated.

The problem has been verified to exist at least for Boost 1.73 and the most recent version 1.74 as well.

The problem was found by a more indirect usage of boost::bind via boost::thread in our code base using this kind of code:

#include <boost/thread.hpp>

struct S
{
  S() 
  {
    boost::thread th(&S::launch_me, this);
  }  

  void launch_me() noexcept {}
};

[pdimov]

Thanks, will fix shortly.

[Dani-Hub]

What a quick reaction - Thanks Peter!