Boost Type Erasure library cannot compile in C++ Builder Windows VCL application

[AndyBell1]

I’m using the type erasure library but have an issue (which I can workaround) when compiling in Windows 10 using Embarcadero C++ Builder 11.3.

My problem is that C++ Builder brings in the Windows SDK Windows.h include file in every Windows VCL UI project it creates before any of my code has compiled and it’s causing conflicts in boost header member11.hpp.

This code is enough to cause the error:

#include <boost/type_erasure/any.hpp>
#include <boost/type_erasure/any_cast.hpp>
#include <boost/type_erasure/builtin.hpp>
#include <boost/type_erasure/operators.hpp>
#include <boost/type_erasure/member.hpp>
#include <boost/type_erasure/free.hpp>
#include <boost/mpl/vector.hpp>

namespace mynamespace {
BOOST_TYPE_ERASURE_MEMBER(ReadStatus)
}

The error is because Windows.h defines ‘interface’ but this code from member11.hpp also uses ‘interface’:

template<class P, template<class ...> class interface, class Sig, class Concept, class Base, class ID>
using choose_member_interface = typename ::boost::mpl::if_c< ::boost::is_reference

::value,
typename ::boost::mpl::if_c< ::boost::type_erasure::detail::is_non_const_ref

::value,
interface<Sig, Concept, Base, const ID>,
Base
>::type,
interface<Sig, Concept, Base, ID>

::type;

and the compiler complains of conflicts.

Embarcadero support have told me that I can’t prevent Windows.h being included in my project before my boost-using code is compiled and attempts I’ve made to circumvent the problem, such as adding these lines to codegear.hpp:

#ifdef interface
#undef interface
#endif

don't work because C++ Builder is still including Windows.h before my code is compiled.

To get around the problem, I changed member11.hpp in my boost installation to

template<class P, template<class ...> class interface_, class Sig, class Concept, class Base, class ID>
using choose_member_interface = typename ::boost::mpl::if_c< ::boost::is_reference

::value,
typename ::boost::mpl::if_c< ::boost::type_erasure::detail::is_non_const_ref

::value,
interface_<Sig, Concept, Base, const ID>,
Base
>::type,
interface_<Sig, Concept, Base, ID>

::type;

Embarcadero support said:
“Boost brings windows.h in because boost pulls it, IF the application is compiled for multi-threading then boost needs to access the OS threading functions, this is when you compile without the VCL.”

and I have confirmed this by creating a simple, multi-threaded Windows console application in C++ Builder…

Joaquin Lopez on the boost-users mailing list asked I raise this as an issue here...

Andy