[Boost.TypeErasure] - Issue compiling under Windows with Embarcadero C++ Builder 11.3

From: Andy Bell (abell_at_[hidden])
Date: 2023-07-03 12:01:57

Hi

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<P>::value,

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

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

        interface_<Sig, Concept, Base, const ID>,

        Base

    >::type,

    interface_<Sig, Concept, Base, ID>

>::type;

which I don't think will have side effects as 'interface/interface_' here is self-contained, but it doesn't feel like a good long term solution. 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...

My question is: Is there a better way to work around this issue? My tests indicate that the Type Erasure library is working properly with my change, but it feels more like a hack than a fix...

Thanks,

Andy Bell
Control Systems & Software Engineer
Tel:          [phone]
Fax:         [phone]
Web:        www.thermcosystems.com<http://www.thermcosystems.com/>  www.csd-epi.com<http://www.csd-epi.com/>

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