Hi, I discovered that the named arguments to class templates cannot be abstract type with Boost 1.34 Here's an example of what I mean: #include <boost/parameter.hpp> struct foo { virtual void not_defined() = 0; }; struct derived_foo : foo {}; BOOST_PARAMETER_TEMPLATE_KEYWORD(param_name) typedef boost::parameter::parameters< boost::parameter::optional< tag::param_name
signature;
template< typename T
struct X { typedef T type; }; template< typename Arg = boost::parameter::void_
struct bar { // Create ArgumentPack typedef typename signature::bind< Arg >::type args; typedef typename boost::parameter::binding< args , tag::param_name, foo
::type type; };
struct foobar : bar< param_name<derived_foo> > // This produces an error //bar< param_name<foo > // Doesn't work either //bar<> // relying on the default seems to work { }; When I try to compile the above code, I get the following errors on VC 7.1: fails_abstract_class.cpp d:\Folders\Projects\boost_1_34_0\boost\parameter\aux_\arg_list.hpp(266) : error C2259: 'derived_foo' : cannot instantiate abstract class due to following members: 'void foo::not_defined(void)' : pure virtual function was not defined d:\Folders\Projects\components\dev\projects\test_boost_param_abstract_classes\test_boost_param_abstract_classes\fails_abstract_class.cpp(4) : see declaration of 'foo::not_defined' d:\Folders\Projects\boost_1_34_0\boost\parameter\binding.hpp(58) : see reference to class template instantiation 'boost::parameter::aux::arg_list<TaggedArg,Next>' being compiled with [ TaggedArg=boost::parameter::aux::make_arg_list0<boost::parameter::aux::make_items<boost::parameter::optional<tag::param_name>,param_name<derived_foo>,boost::parameter::aux::make_items<boost::parameter::void_,boost::parameter::void_,boost::parameter::aux::make_items<boost::parameter::void_,boost::parameter::void_,boost::parameter::aux::make_items<boost::parameter::void_,boost::parameter::void_,boost::parameter::aux::make_items<boost::parameter::void_,boost::parameter::void_,boost::mpl::identity<boost::parameter::void_>>>>>>::type,boost::parameter::parameters<boost::parameter::optional<tag::param_name>>::deduced_list,boost::parameter::aux::tag_template_keyword_arg,boost::mpl::true_,boost::parameter::aux::set0,boost::parameter::aux::empty_arg_list,boost::parameter::void_>::tagged, Next=boost::parameter::aux::empty_arg_list ] d:\Folders\Projects\components\dev\projects\test_boost_param_abstract_classes\test_boost_param_abstract_classes\fails_abstract_class.cpp(40) : see reference to class template instantiation 'boost::parameter::binding<Parameters,Keyword,Default>' being compiled with [ Parameters=bar<param_name<derived_foo>>::args, Keyword=tag::param_name, Default=foo ] d:\Folders\Projects\components\dev\projects\test_boost_param_abstract_classes\test_boost_param_abstract_classes\fails_abstract_class.cpp(46) : see reference to class template instantiation 'bar<Arg>' being compiled with [ Arg=param_name<derived_foo> ] d:\Folders\Projects\boost_1_34_0\boost\parameter\aux_\arg_list.hpp(272) : error C2259: 'derived_foo' : cannot instantiate abstract class due to following members: 'void foo::not_defined(void)' : pure virtual function was not defined d:\Folders\Projects\components\dev\projects\test_boost_param_abstract_classes\test_boost_param_abstract_classes\fails_abstract_class.cpp(4) : see declaration of 'foo::not_defined' d:\Folders\Projects\boost_1_34_0\boost\parameter\aux_\arg_list.hpp(355) : error C2259: 'derived_foo' : cannot instantiate abstract class due to following members: 'void foo::not_defined(void)' : pure virtual function was not defined d:\Folders\Projects\components\dev\projects\test_boost_param_abstract_classes\test_boost_param_abstract_classes\fails_abstract_class.cpp(4) : see declaration of 'foo::not_defined' d:\Folders\Projects\boost_1_34_0\boost\parameter\aux_\arg_list.hpp(361) : error C2259: 'derived_foo' : cannot instantiate abstract class due to following members: 'void foo::not_defined(void)' : pure virtual function was not defined d:\Folders\Projects\components\dev\projects\test_boost_param_abstract_classes\test_boost_param_abstract_classes\fails_abstract_class.cpp(4) : see declaration of 'foo::not_defined' d:\Folders\Projects\boost_1_34_0\boost\parameter\aux_\arg_list.hpp(367) : error C2259: 'derived_foo' : cannot instantiate abstract class due to following members: 'void foo::not_defined(void)' : pure virtual function was not defined d:\Folders\Projects\components\dev\projects\test_boost_param_abstract_classes\test_boost_param_abstract_classes\fails_abstract_class.cpp(4) : see declaration of 'foo::not_defined' However, if I rely on the default established when binding the argument, everything just works. Is there something I'm doing wrong? For now I have a workaround. I wrap the argument types in mpl::identity and extract them again afterwards. This works, but it is not pretty. #include <boost/parameter.hpp> #include <boost/mpl/identity.hpp> struct foo { virtual void not_defined() = 0; }; struct derived_foo : foo {}; BOOST_PARAMETER_TEMPLATE_KEYWORD(param_name) typedef boost::parameter::parameters< boost::parameter::optional< tag::param_name
signature;
template< typename T
struct X { typedef T type; }; template< typename Arg = boost::parameter::void_
struct bar { // Create ArgumentPack typedef typename signature::bind< boost::mpl::identity<Arg> >::type args; typedef typename boost::parameter::binding< args , tag::param_name, boost::mpl::identity<foo>
::type type_provider;
typedef typename type_provider::type type; }; struct foobar : bar< param_name<derived_foo> > //bar<> { }; Any thoughts on this one? Thanks, Sven