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

From: Larry Evans (cppljevans_at_[hidden])
Date: 2008-03-12 07:29:23

On 03/12/08 06:10, Larry Evans wrote:
> On 03/11/08 22:42, Max Motovilov wrote:
> [snip]
>> I apologize in advance if something along these lines is already 
>> available; however current public documentation doesn't mention such a 
>> facility and a brief glance into SVN did not reveal one either...
>>
>> product_view
>>
>> Description: provides a view of a Cartesian product of multiple 
>> sequences. Modeled after zip_view in that it expects a sequence [of 
>> length n] of sequences S1...Sn as its argument and lazily generates a 
>> sequence [of length Prod{1...n}( size< Si > )] of sequences 
>> S1[1]...Sn[1] through S1[n]...Sn[n]. Whew... I know I can write better 
>> documentation than that if I put my mind to it :(
>>
>  From Prod[1..n}(size<Si>} it appears this just flattens a list 1 level.
> IOW:
>    from:
>       list
>       < list< A0_0, A0_1>
>       , list< A1_0, A1_1>
>       ...
>       , list< An_0, An_1.
>       >
>    it produces:
>       list
>       < A0_0, A0_1
>       , A1_0, A1_1
>       ...
>       , An_0, An_1
>       >
> 
> Is that right?
>
OOPS, that would be Sum{1..n}(size<Si>} so I guess this would be
more like an outer-product where for:

Input:
   list
   < list<A0_0, A0_1> //S1
   , list<A1_0, A1_1> //S2
   >
Output:
   list
   < list<A0_0, A1_0> //s1[1]...S1[2]? Nope, this is S1[1]...S2[1]
   , list<A0_0, A2_0>
   , list<A0_1, A1_0>
   , list<A0_1, A1_1>
   >

Here, since sizes of inputs are 2 and 2, size of output is 2*2=4.
But that's inconsistent with:

   sequences S1[1]...Sn[1] through S1[n]...Sn[n]

Could you please clarify?  I'm lost ;(