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

From: Larry Evans (cppljevans_at_[hidden])
Date: 2008-03-12 10:29:47

On 03/12/08 08:22, Max Motovilov wrote:
[snip]
>> A solution is posted here:
>>
>> http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?CPPTM_Answers_-_Exercise_7-8
>>
>> It would be interesting to compare the two solutions.  The exercise just
>> specified 2 input sequences whereas your's allows (I guess)
>> any n>0 number of input sequences.
> 
> 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. 
[snip]
 From one of your previous post's, the output is a crossproduct which
requires a nested for_each loop to printout first the rows
and for each row the elements in that row.  That's the only reason
for the static print_each and struct element_printer.
I realize now that should have been commented to indicate it was
not part of the solution but only used to demonstrate the
correctness, which I hoped the printout:

Running 2 test cases...
row.col=0.100
row.col=0.101
row.col=0.102
...

would have demonstrated.

Also, I am not sure that cross_product_view:

    does not provide an actual sequence adapter

because the superclass of cross_product_view is a transform_view and the
first page of chapter 7 states:

   A sequence view ... is a lazy adapter

So, in view of that, could you explain why it's not a sequence adapter?