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

From: Larry Evans (cppljevans_at_[hidden])
Date: 2008-03-12 15:40:53

On 03/12/08 09:56, Max Motovilov wrote:
>>> No, they don't look similar. As far as I can tell from a one-minute 
>>> look, the solution is simply a nested for_each loop and does not provide 
>>> an actual sequence adapter, despite the name cross_product_view. 
> 
> That's the danger of one-minute looks... I take that back. Yes, the 
> whole thing is a sequence and output pairs are indeed lazily generated. 
> I am not sure if this approach can be generalized to an arbitrary number 
> of sequences. Perhaps it can be, by making the whole thing a recursive 
> template instead of 3 separate ones. I'd try it just to see which 
> version results in simpler code (gut feeling: the recursive template) 
> and in faster compilation times (gut feeling: my current implementation) 
> but customers and management are jointly snapping at my heels...
> 
>> So, in view of that, could you explain why it's not a sequence adapter?
> 
> The usual explanation: needed more coffee :)
>

I'm afraid I was wrong.  here's what I get as the transform output with
my type_name_print:

test_product
boost::mpl::cross_product_view
< boost::mpl::range_c
   < int
   , 0
   , 3
   >
, boost::mpl::range_c
   < int
   , 100
   , 104
   >
 >

where the function producing this is:

typedef mpl::range_c<int,0,3> seq0;
typedef mpl::range_c<int,100,104> seq1;

void test_product(void)
{
     std::cout<<"test_product\n";
     typedef mpl::cross_product_view<seq0,seq1> type;
   #ifdef TYPE_TREE_PRINT
     ::utility::type_name_print<type>();
   #else
     type::print_each();
   #endif
}

and with #define TYPE_TREE_PRINT. Which I expected to see was something 
contains pair's of mpl::integral_c<int,I>.

So..., the code I posted is useless :(
Sorry for noise.  Back to drawing board.