Compile errors with boost::mpl::if on MinGW/Msys
Hi, I'm trying to use typedef typename boost::mpl::if_ to choose between two structures, both with identical function names, so I can choose which function to call based on the template parameter type. The code works fine on Visual Studio 2005. But in MinGW/MSys it returns: RPC3_Boost.h:203: error: template argument 2 is invalid RPC3_Boost.h:203: error: template argument 3 is invalid RPC3_Boost.h:203: error: ISO C++ forbids declaration of `type' with no type This is with boost_1_35_0. I've cut out as much code as I can: struct ReadBitstream { static void apply(RakNet::BitStream &bitStream, RakNet::BitStream* t) {/* ... */} }; template <typename T> struct ReadPtr { static inline void apply(RakNet::BitStream &bitStream, const char *&t) {applyStr(bitStream, (char *&) t);} }; template< typename T > struct DoRead { typedef typename boost::mpl::if_< boost::is_convertible<T*,RakNet::BitStream*>, typename ReadBitstream, typename ReadPtr<T> >::type type; }; To call the function, I use: DoRead< boost::remove_pointer<T>::type >::type::apply(* (args.bitStream),&t); Thanks in advance for any help. The whole file is here if you need to see more code: https://raknetjenkinsso.svn.sourceforge.net/svnroot/raknetjenkinsso/trunk/De...
________________________________________ De: boost-users-bounces@lists.boost.org [boost-users-bounces@lists.boost.org] En nombre de Kevin Jenkins [gameprogrammer@rakkar.org] Enviado el: miércoles, 03 de septiembre de 2008 16:47 Para: boost-users@lists.boost.org Asunto: [Boost-users] Compile errors with boost::mpl::if on MinGW/Msys
Hi,
I'm trying to use typedef typename boost::mpl::if_ to choose between two structures, both with identical function names, so I can choose which function to call based on the template parameter type.
The code works fine on Visual Studio 2005. But in MinGW/MSys it returns:
RPC3_Boost.h:203: error: template argument 2 is invalid RPC3_Boost.h:203: error: template argument 3 is invalid RPC3_Boost.h:203: error: ISO C++ forbids declaration of `type' with no type [...] typename ReadBitstream, typename ReadPtr<T> >::type type;
I'd say those typenames should go. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo
Kevin Jenkins wrote:
Hi,
I'm trying to use typedef typename boost::mpl::if_ to choose between two structures, both with identical function names, so I can choose which function to call based on the template parameter type. <snip>
template< typename T > struct DoRead { typedef typename boost::mpl::if_< boost::is_convertible<T*,RakNet::BitStream*>, typename ReadBitstream, typename ReadPtr<T> >::type type; };
You only use typename before a type that is dependant on an template parameter. In this case it is clear that ReadBitStream and ReadPtr<T> are types regardless of what type is substituted for T. Usually typename is required for nested types, since template specialization can completely change those I guess. Microsoft is very lax about enforcing this, so you can get away with extra typename and sometimes, IIRC, missing typename keywords. Try this (untested) template< typename T > struct DoRead : boost::mpl::if_< boost::is_convertible<T*,RakNet::BitStream*>, ReadBitstream, ReadPtr<T> > {};
participants (3)
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JOAQUIN M. LOPEZ MUÑOZ
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John C. Femiani
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Kevin Jenkins