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

6 Feb 2010

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-----Original Message-----
From: boost-users-bounces@lists.boost.org [mailto:boost-users-
bounces@lists.boost.org] On Behalf Of Larry Evans
Sent: 31 January 2010 18:04
To: boost-users@lists.boost.org
Subject: Re: [Boost-users] generate structs with all combinations of
members from a given struct
[snip]
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Because all the members of params are double, there is no way to
differentiate between different the 1st and 2nd vector<double>
Yes; however, Couldn't you, pair each type with it's index?
IOW, you have, instead of:
typedef
    package_c::pkg_type
  fields_t
  ;
Larry,

I have finally reached a Boost.PP based solution which I describe below. I
will then go back to your fusion-based solution.
My point is to compare compile-time, memory requirement of the compiler and
ease of use of the generated types.

Here is my solution (the attached files compiles and preprocesses at least
under g++4.4 with:   g++ -E -c structcombos.cpp).

With

   struct S {
      int m1;
      double m2;
      double m3;
   };

the user is required to define the macro

#define struct_members_seq ((int,m1))((double,m2))((double,m3))

then calls the macro

STRUCT_MEMBERS_COMBINATIONS_SEQ(struct_members_seq)

This expands to 
struct params_m3 { double m3; }; struct params_m2 { double m2; }; struct
params_m2_m3 { double m2; double m3; }; struct params_m1 { int m1; }; struct
params_m1_m3 { int m1; double m3; }; struct params_m1_m2 { int m1; double
m2; }; struct params_m1_m2_m3 { int m1; double m2; double m3; };

Questions:
1. It takes a little while to preprocess. Are there optimizations that are
visible in the attached file?
2. How do I obtain some vertical appearance that is easier to read? Can I
generate the newline somehow?

Regards,

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

Hicham Mouline