Gesendet: Mittwoch, 01. Februar 2017 um 17:04 Uhr Von: "Peter Dimov" An: boost@lists.boost.org Betreff: Re: [boost] [factory][bind] C2664 with MSVC 2015 & 1.63

Jens Weller wrote:

...

Hello Boost,

I'm having this Problem: http://lists.boost.org/boost-users/2015/04/84176.php

That message already describes pretty much what I see, except that I use 1.63 and the latest 2015 VC++.

Can you please give me a short but complete program that fails with the same or a similar error?

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Hi Peter, yes, I managed to that by now: #include #include #include struct Widget {}; struct Panel: Widget{Panel(Widget* q){}}; using make_interface = boost::function; void registerType(const make_interface &make) { //factory.register_factory(type_id,make); } int main(int argc, char *argv[]) { auto f = boost::factory(); registerType( boost::bind(f,_1));//< this line is the cause, factory it self compiles } Error: boost\bind\bind.hpp:249: error: C2664: 'Panel *boost::factory::operator ()(void) const': cannot convert argument 1 from 'Widget *' to 'Widget *&' thanks, Jens Weller Adding the full error message from compiler output here: D:\cpp\libraries\boost_1_63_0\boost/bind/bind.hpp(249): error C2664: 'Panel *boost::factory::operator ()(void) const': cannot convert argument 1 from 'Widget *' to 'Widget *&' D:\cpp\libraries\boost_1_63_0\boost/bind/bind.hpp(1306): note: see reference to function template instantiation 'R *boost::_bi::list1>::operator ()(boost::_bi::type,F &,A &,long)' being compiled with [ R=Panel *, F=boost::factory, A1=Widget *, A=boost::_bi::rrlist1 ] D:\cpp\libraries\boost_1_63_0\boost/bind/bind.hpp(1306): note: see reference to function template instantiation 'R *boost::_bi::list1>::operator ()(boost::_bi::type,F &,A &,long)' being compiled with [ R=Panel *, F=boost::factory, A1=Widget *, A=boost::_bi::rrlist1 ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(138): note: see reference to function template instantiation 'Panel *boost::_bi::bind_t,boost::_bi::list1>>::operator ()<T>(A1 &&)' being compiled with [ T=Widget *, A1=Widget * ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(138): note: see reference to function template instantiation 'Panel *boost::_bi::bind_t,boost::_bi::list1>>::operator ()<T>(A1 &&)' being compiled with [ T=Widget *, A1=Widget * ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(132): note: while compiling class template member function 'Widget *boost::detail::function::function_obj_invoker1::invoke(boost::detail::function::function_buffer &,T0)' with [ FunctionObj=boost::_bi::bind_t,boost::_bi::list1>>, R=Widget *, T0=Widget * ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(936): note: see reference to function template instantiation 'Widget *boost::detail::function::function_obj_invoker1::invoke(boost::detail::function::function_buffer &,T0)' being compiled with [ FunctionObj=boost::_bi::bind_t,boost::_bi::list1>>, R=Widget *, T0=Widget * ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(936): note: see reference to class template instantiation 'boost::detail::function::function_obj_invoker1' being compiled with [ FunctionObj=boost::_bi::bind_t,boost::_bi::list1>>, R=Widget *, T0=Widget * ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(727): note: see reference to function template instantiation 'void boost::function1::assign_to<Functor>(Functor)' being compiled with [ R=Widget *, T0=Widget *, Functor=boost::_bi::bind_t,boost::_bi::list1>> ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(727): note: see reference to function template instantiation 'void boost::function1::assign_to<Functor>(Functor)' being compiled with [ R=Widget *, T0=Widget *, Functor=boost::_bi::bind_t,boost::_bi::list1>> ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(1073): note: see reference to function template instantiation 'boost::function1::function1<Functor>(Functor,int)' being compiled with [ R=Widget *, T0=Widget *, Functor=boost::_bi::bind_t,boost::_bi::list1>> ] D:\cpp\libraries\boost_1_63_0\boost/function/function_template.hpp(1072): note: see reference to function template instantiation 'boost::function1::function1<Functor>(Functor,int)' being compiled with [ R=Widget *, T0=Widget *, Functor=boost::_bi::bind_t,boost::_bi::list1>> ] ..\msvctestbed\main.cpp(19): note: see reference to function template instantiation 'boost::function::function,boost::_bi::list1>>>(Functor,int)' being compiled with [ Functor=boost::_bi::bind_t,boost::_bi::list1>> ] ..\msvctestbed\main.cpp(19): note: see reference to function template instantiation 'boost::function::function,boost::_bi::list1>>>(Functor,int)' being compiled with [ Functor=boost::_bi::bind_t,boost::_bi::list1>> ]

Gesendet: Mittwoch, 01. Februar 2017 um 20:34 Uhr Von: "Peter Dimov" An: boost@lists.boost.org Betreff: Re: [boost] [factory][bind] C2664 with MSVC 2015 & 1.63

Jens Weller wrote:

...

Hi Peter,

yes, I managed to that by now: #include #include #include

struct Widget {}; struct Panel: Widget{Panel(Widget* q){}};

using make_interface = boost::function; void registerType(const make_interface &make) { //factory.register_factory(type_id,make); } int main(int argc, char *argv[]) { auto f = boost::factory(); registerType( boost::bind(f,_1));//< this line is the cause, factory it self compiles }

Thanks Jens.

When I try

registerType( f );

I get the same error:

1>testbed2015.cpp(6): warning C4100: 'q': unreferenced formal parameter 1>testbed2015.cpp(10): warning C4100: 'make': unreferenced formal parameter 1>c:\Projects\boost-git\boost\boost/function/function_template.hpp(138): error C2664: 'Panel *boost::factory::operator ()(void) const': cannot convert argument 1 from 'Widget *' to 'Widget *&'

The problem as far as I can see is that boost::function passes its parameter of type Widget* as an rvalue to its target, rather than as an lvalue, and factory<> takes its arguments by lvalue reference.

function's behavior is correct in that if you declare boost::function, the argument needs to be passed as an rvalue or it won't work. But it does break code such as the above.

Ideally, boost::factory would need to be fixed to use perfect forwarding on C++11 and above.

A quick look at its documentation suggests using forward_adapter:

auto f2 = boost::forward_adapter( f ); registerType( f2 ); // works

forward_adapter however doesn't define ::result_type so when you bind it you have to give the type:

registerType( boost::bind( f2, _1 ) );

No idea why it needs to be so hard.

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Yes, that fixes this indeed. Didn't know about forward_adapter. thanks, Jens Weller