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

-----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users- bounces@lists.boost.org] On Behalf Of Larry Evans Sent: 09 February 2010 18:11 To: boost-users@lists.boost.org Subject: Re: [Boost-users] generate structs with all combinations of members from a given struct

Hmmm. What about multi_array_base being the S_empty:

struct S_empty{};

IOW, this would be the 32nd version of S. Your PP method now generates 31 versions, you could just add the 32 version be S_empty.

This makes sense because each time a field is added, it's like a derived class. IOW, S_empty would be the base class, and all other classes would be derived from it. I vaguely remember reading about that somewhere, IOW, that adding a field to a class is sorta like restricting the class is sorta like deriving from that class. It's not the Ss themselves that I need to derive from a base class to transport through translation units. It's boost::multi_array that I need to transport anonymously. And that is why I wrap the multi_array in a struct that derives from multi_array_base.

...

I have say 5 translation units tr1,tr2,tr3,tr4 and tr5.

The specific multi_array is generated in tr1. It needs to pass via tr2,tr3 and tr4 to reach tr5. tr2,3 and 4 do not need to know what exact multi_array type it is, so they just deal with multi_array_base. tr5 then dynamic casts the multi_array_base ref to the appropriate multi_array with the appropriate S.

pseudo_code tr1, itself geenrate switch( bitset.toulong() ) { case 1: some_function( multi_array_adapted_to_derive_from_base& ); case 2: some_function( multi_array_adapted_to_derive_from_base& ); .... case 63: some_function( multi_array_adapted_to_derive_from_base& ); }

This is still work in progress.

I'd be interesting in seeing this code when you're done with it. I'd like to try using:

composite_tagged_seq < all_of_aligned , field_I1 , field_I2 ... , field_In

...

where field_I1...field_In is some subset of S::field1,...field5 and composite_tagged is from composite_tagged_seq.zip in the boost vault:

http://www.boostpro.com/vault/index.php?&directory=Data Structures

Then compare the compile-time and run-time performance. I've no doubt it would be slower than the PP version, but I'm just curious about how much.

-regards, Larry I will definitely compare as well once I understand what you mean.

I have another problem for now. PP processing is starting to be slow, I need help to optimize it. Attached in the PP code. Also, in the above, all the Ss need to be generated only once. However, in multi_array, the N depends on the translation unit. I will have like 100 translation units, each with a different N. If I were to include the PP code to generate the Ss in each of the 100 trs, it would repeat the preprocessing uselessly. I need to run the first part of the PP just once, then the 2nd part of the PP that generates the multi_arrays for each of the 100 tr units. Is this possible? Regards,