Boost bind fails with Xcode13(clang version 13.0.0)

[kkumar45]

I am seeing failures when using boost::lambda::bind with std::function in Xcode13(clang version 13.0.0). I have created a sample program that can shows the failure details.

#include <functional>
#include <boost/lambda/bind.hpp>

void func() {}

int main() {
    auto var = std::function<void()>(boost::lambda::bind(func));
}

It seems to be that the template lambda_functor_base is undefined. In digging through Boost, I cannot find a definition of the initial template. There's a forward declaration, and explicit instantiations, but no default definition. If I add a default definition (uncomment in the godbolt example below), it suddenly starts compiling. Any thoughts on it?

https://godbolt.org/z/hx97Gova8

Error details:

In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:140:31: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
class lambda_functor : public T 
                              ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/type_traits:2680:83: note: in instantiation of template class 'boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>>' requested here
struct _LIBCPP_TEMPLATE_VIS is_assignable : _BoolConstant<__is_assignable(_Tp, _Up)> { };
                                                                                  ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/type_traits:2722:14: note: in instantiation of template class 'std::is_assignable<const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>> &, const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>> &>' requested here
    : public is_assignable<typename add_lvalue_reference<_Tp>::type,
             ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/type_traits:505:28: note: in instantiation of template class 'std::is_copy_assignable<const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>> &>' requested here
__expand_to_true<_EnableIf<_Pred::value>...> __and_helper(int);
                           ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/type_traits:509:44: note: while substituting explicitly-specified template arguments into function template '__and_helper' 
using _And _LIBCPP_NODEBUG_TYPE = decltype(__and_helper<_Pred...>(0));
                                           ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/tuple:952:26: note: in instantiation of template type alias '_And' requested here
    tuple& operator=(_If<_And<is_copy_assignable<_Tp>...>::value, tuple, __nat> const& __tuple)
                         ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/tuple:1267:1: note: in instantiation of template class 'std::tuple<const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>> &>' requested here
forward_as_tuple(_Tp&&... __t) _NOEXCEPT
^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/__functional/function.h:155:44: note: in instantiation of function template specialization 'std::forward_as_tuple<const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>> &>' requested here
        : __f_(piecewise_construct, _VSTD::forward_as_tuple(__f),
                                           ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/__functional/function.h:286:11: note: in instantiation of member function 'std::__function::__alloc_func<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, std::allocator<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>, void ()>::__alloc_func' requested here
        : __f_(__f, _VSTD::move(__a)) {}
          ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/__functional/function.h:312:33: note: in instantiation of member function 'std::__function::__func<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, std::allocator<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>, void ()>::__func' requested here
    ::new ((void*)__hold.get()) __func(__f_.__target(), _Alloc(__a));
                                ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/__functional/function.h:289:14: note: in instantiation of member function 'std::__function::__func<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, std::allocator<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>, void ()>::__clone' requested here
    explicit __func(_Fp&& __f, _Alloc&& __a)
             ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/__functional/function.h:405:44: note: in instantiation of member function 'std::__function::__func<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, std::allocator<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>, void ()>::__func' requested here
                    ::new ((void*)&__buf_) _Fun(_VSTD::move(__f), _Alloc(__af));
                                           ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/__functional/function.h:420:11: note: in instantiation of function template specialization 'std::__function::__value_func<void ()>::__value_func<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, std::allocator<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>' requested here
        : __value_func(_VSTD::forward<_Fp>(__f), allocator<_Fp>()) {}
          ^
/opt/compiler-explorer/clang-13.0.0/bin/../include/c++/v1/__functional/function.h:1118:50: note: in instantiation of function template specialization 'std::__function::__value_func<void ()>::__value_func<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, void>' requested here
function<_Rp(_ArgTypes...)>::function(_Fp __f) : __f_(_VSTD::move(__f)) {}
                                                 ^
<source>:17:12: note: in instantiation of function template specialization 'std::function<void ()>::function<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, void>' requested here
auto var = std::function<void()>(boost::lambda::bind(func));
           ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:162:5: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
    inherited::template sig<null_type>::type
    ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:191:12: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  typename inherited::template sig<tuple<A&> >::type
           ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:199:37: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  BOOST_LAMBDA_DISABLE_IF_ARRAY1(A, inherited::template sig<tuple<A const&> >)
                                    ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:207:12: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  typename inherited::template sig<tuple<A&, B&> >::type
           ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:215:40: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  BOOST_LAMBDA_DISABLE_IF_ARRAY2(A, B, inherited::template sig<tuple<A const&, B&> >)
                                       ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:223:40: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  BOOST_LAMBDA_DISABLE_IF_ARRAY2(A, B, inherited::template sig<tuple<A&, B const&> >)
                                       ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:231:40: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  BOOST_LAMBDA_DISABLE_IF_ARRAY2(A, B, inherited::template sig<tuple<A const&, B const&> >)
                                       ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:239:12: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  typename inherited::template sig<tuple<A&, B&, C&> >::type
           ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:248:43: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  BOOST_LAMBDA_DISABLE_IF_ARRAY3(A, B, C, inherited::template sig<tuple<A const&, B const&, C const&> >)
                                          ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
In file included from <source>:1:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/bind.hpp:15:
In file included from /opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/core.hpp:57:
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_functors.hpp:258:12: error: implicit instantiation of undefined template 'boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>, boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<1, boost::lambda::function_action<1, void>>, boost::tuples::tuple<void (&)()>>>>>'
  typename inherited::template sig<tuple<CALL_REFERENCE_TYPES> >::type
           ^
/opt/compiler-explorer/libs/boost_1_75_0/boost/lambda/detail/lambda_fwd.hpp:38:7: note: template is declared here
class lambda_functor_base;
      ^
11 errors generated.

[kkumar45]

Can someone take a look at it?

[pdimov]

The reason this fails is because libc++ tries to instantiate std::is_assignable, which checks whether operator= exists, which for lambda function objects is overloaded, but its definition isn't included by <boost/lambda/bind.hpp>. This can be fixed if the appropriate headers are included in bind.hpp, as in https://godbolt.org/z/YsEnEK7qP.

Interestingly, if I include <boost/lambda/lambda.hpp> instead, as in https://godbolt.org/z/cWh9vooaP, it fails because of a bug in libc++ - it uses operator& directly in its implementation, instead of std::addressof. Attn @mclow. :-)

[mclow]

See https://reviews.llvm.org/D116380 for libc++ change.