Re: [boost] Proposed: a new sequence adapter for MPL (product_view)

From: Max Motovilov (max_at_[hidden])
Date: 2008-03-12 19:33:50

Ok, I have the recursive equivalent of my original implementation now. 
About 2/3 in length, perhaps marginally easier to understand. However 
2^7 combinations kick it (with VStudio 2008) into never-never-land and 
the iterative solution takes it in stride, if not instantaneously.

So, do you think this thingie belongs in MPL?

...Max...

=====================================================================================

template< typename S > struct flatten_view;

template< typename S >
struct flatten_descend_once
{
        typedef joint_view<
                typename front<S>::type,
                flatten_view<
                        iterator_range<
                                typename next<
                                        typename begin< S >::type
				>::type,
                                typename end< S >::type
			>
		>
	>
                type;
};

template< typename S >
struct flatten_view :
        public eval_if<
                typename empty<S>::type,
                identity<S>,
                flatten_descend_once<S>
	>::type
{
                typedef flatten_view type;
};

template< typename S, typename A> struct product_view_ex;

template< typename S, typename A >
struct product_descend_once
{
        typedef flatten_view< transform_view<
                typename front<S>::type,
                product_view_ex<
                        typename pop_front<S>::type,
                        push_front<A,_1>
		>
	> >
                type;
};

template< typename S, typename A>
struct product_view_ex :
        public eval_if<
            typename empty<S>::type,
                push_back< S, A>,
                product_descend_once< S, A >
	>::type		
{
        typedef product_view_ex type;
};

template< typename S> struct product_view :
        public if_<
                typename empty<S>::type, S,	
                product_view_ex< S, typename clear<S>::type >
	>::type
{
        typedef product_view type;
};