Re: [Boost-users] generate structs with all combinations of members from a given struct

Subject: Re: [Boost-users] generate structs with all combinations of members from a given struct
From: Larry Evans (cppljevans_at_[hidden])
Date: 2010-01-30 19:24:11

On 01/30/10 13:35, Larry Evans wrote:
> On 01/30/10 00:37, Hicham Mouline wrote:
>> Hello,
>>  
>> struct params {
>>   double field1;
>>   double field2;
>>   double field3;
>>   double fiedl4;
>> };
>>  
>> I would like to generate all the types that hold any combination of 
>> the members of params.
> [snip]
> 
> Step1:
>   Create cross-product of void and {field1,field2,...}.
>   This will produce a sequence of pairs:
> 
>    no_yes =
>      ( (void,field1)
>      , (void,field2)
>      ...
>      , (void,fieldn)
>      )
> 
> Step2:
> 
>   Create the crosss product of all rows in no_yes.
> 
>   cross_no_yes =
>     ( (void,void,..void)
>     , (field1,void,...void)
>     , (void,field2,void...,void)
>     ...
>     , (field1,field2,...fieldn)
>     )
> 
> step3:
> 
>   remove all the voids in all the rows of cross_no_yes.
> 
> Since the size<no_yes> == n and each element in that row is size 2,
> the cross_no_yes size would be 2^n.  Then simply rm the all void row.
> 
> Not tested.
Now tested.  The attached produces:

/home/evansl/prog_dev/boost-svn/ro/trunk/sandbox-local/build/gcc4_4v/sandbox/variadic_templates/libs/mpl/sandbox/list_comprehension~subsets.exe 

absent_fields_seq=
( Absent=9000, Field=9001)
( Absent=9000, Field=9002)
( Absent=9000, Field=9003)
size<select_fields_seq>::value=8
select_fields_seq=
{ 9000, 9000, 9000}
{ 9000, 9000, 9003}
{ 9000, 9002, 9000}
{ 9000, 9002, 9003}
{ 9001, 9000, 9000}
{ 9001, 9000, 9003}
{ 9001, 9002, 9000}
{ 9001, 9002, 9003}

Compilation finished at Sat Jan 30 18:17:41

9000 indicates absence of a field.  900I, for I>0,
indicates presence of the I-th field.

HTH.

-regards,
Larry