On 02/28/2005 06:35 PM, David Abrahams wrote:
Larry Evans <cppljevans@cox-internet.com> writes:
On 02/28/2005 10:01 AM, David Abrahams wrote: [snip]
You're folding some kind of cons cell, right? Don't you want to implement begin and end on that? template <class A, class B> struct begin<inherit<A,B> > { ... }; or something?
Yes. But how do I know what A or B is.
??
At the point of ... the compiler knows what they are
So, I tried: //{--------- cut-here -------- template < template<typename,typename>class ForwardOpTmpl , typename LeftArg , typename RightArg
struct begin < ForwardOpTmpl<LeftArg,RightArg> > { typedef ForwardOpTmpl<LeftArg,RightArg> type; }; template < template<typename,typename>class ForwardOpTmpl , typename LeftArg , typename RightArg
struct next < ForwardOpTmpl<LeftArg,RightArg> > { typedef RightArg type; }; //}--------- cut-here -------- But intel-linux said next was ambiguous. Also, the above code assumes the last arg to fold was: ForwardOpTmpl<arg<2>,arg<1> > I was hoping to be more general, but maybe just for my test, it would be OK.
It has to be the result of size<Sequence>-1 applications of ForwardOp.
Do you mean that you want to restrict the partial specialization matching to only match your tuple types? You don't have to use inherit directly, you know; you could just derive your own my_inherit class from it and match that in the partial specialization. If you only use my_inherit to build these tuples, you're home free.
Replacing ForwardOpTmpl with my_inherit, defined as: template< typename Left, typename Right> struct my_inherit: inherit2<Left,Right> { typedef my_inherit type; }; still got the ambiguous error message with intel-linux. gcc gave some other error message. Even if the above did, work, I'd need an end specialization, and that would involve knowing the 2nd arg to fold; hence, the specialization would have to be: template<typename Sequence, typename Start, typename ForwardOp> struct end<fold<Sequence,Start,ForwardOp>::type> { ... }; which is doomed to fail (AFAICT) because of the non-deduced context. Or am I missing something again?