Re: [Boost-users] Problem with type traits

Robert Dailey wrote:

Hi,

I'm trying to create my own struct that is compatible with boost::mpl::or_ as well as boost::enable_if.

I find that using boost::mpl::or_ requires that my structure have a 'type' member, and enable_if looks for 'value'. Must I define both? What is the proper way to handle this? Below is my structure:

template< typename t_type > struct is_sink { typedef typename boost::mpl::or_< vfx::io::is_device, boost::is_same > type; };

The above structure works perfectly fine with boost::mpl::or_, but does not work for boost::enable_if because it is looking for a 'value' member. I feel what it should be looking for is is_sink::type::value. An example of how I use the above structure is below:

template< typename t_source, typename t_data > typename boost::enable_if< boost::mpl::and_<*is_source*, boost::is_pod >, t_source

...

::type& operator>> ( t_source& source, t_data& data ) { source.Read( reinterpret_castboost::uint8_t*( &data ), sizeof( t_data ) ); return source; } I think the condition has to satisfy this concept: http://www.boost.org/doc/libs/1_35_0/libs/mpl/doc/refmanual/integral-constan...

Anyhow, I think it is a lot easier in general to use inheritance for metafunctions: i.e. (untested) template< typename t_type > struct is_sink: ::boost::mpl::or_< ::vfx::io::is_device, ::boost::is_same >::type {}; -- John Femiani