AMDG Scott Meyers wrote:
Steven Watanabe wrote:
template<class Sequence> struct MakeFeatures { typedef Features<typename copy<Sequence, back_inserter<vector0<> >
::type> type; };
I'm trying to understand the code you posted, but I'm having trouble, probably because I'm missing some basic concepts. I hope people here won't mind helping me with something I'm sure is basic: why do we need to make a copy of Sequence here? I've tried replacing the above typedef with
typedef Features<Sequence> type;
and everything breaks, so it's clear that the copy is there for a reason, but what is it?
The copy is to guarantee uniqueness. If you have a Features<mpl::list<...> > this will not be the same as a Features<mpl::vector<...> >. The mpl::copy<> makes sure that Features<> always holds a type built by push_back on vector0<>. Thus, MakeFeatures<mpl::list<int, char, double> >::type is the same as MakeFeatures<mpl::vector<int, char double> >::type. Does that help? In Christ, Steven Watanabe