Re: [Boost-users] Needs advices on design ( mpl or processor )

7 Jan 2012


      On 01/07/12 02:42, Allan Nielsen wrote:
...
On Sat, Jan 7, 2012 at 1:54 AM, Larry Evans  wrote:
...
On 01/06/12 16:19, Allan Nielsen wrote:
...
My problem is not to calculate the actually size, but move the
calculation from the instantiation into the definition of the library.
I have not idea what this means.
Please clarify.
First of all, thanks for your input.
I will try to illustrate my design problem in a more simple example:
struct TagA {
   enum Size { size = 4 };
   enum E { A0  =  0, A1  =  1, A2  =  2, A3  =  3, };
};
struct TagB {
   enum Size { size = 4 };
   enum E { B0  =  0, B1  =  1, B2  =  2, B3  =  3, };
};
struct TagC {
   enum Size { size = 4 };
   enum E { C0  =  0, C1  =  1, C2  =  2, C3  =  3, };
};
// Simple edition of CompressedEnum, but has the same problem
Sorry, what was that problem again?
...
template
struct CompressedEnum {
    enum O { offset = OFFSET };
    enum S { size = T::size };
    T get( ) { ... }
};
// Simple edition of CompressedEnums, but has the same problem
template < typename B0, typename B1, typename B2 >
struct CompressedEnums: public B0, B1, B2 {
    template < typename T> get() { ... }
};
void example1()
{
    // As you see, the expresions for calculating the offset get quite long,
    // and are not easy to maintain.
Here's where I don't understand why the calculation are done outside
the temple and then passed as args to the template.
Why not have a template do the calculations and accumulate the results,
somewhat like mpl::fold or the code I posted earlier?
...
C< CompressedEnum,
CompressedEnum::offset *
                            CompressedEnum::size >,
CompressedEnum
CompressedEnum::offset *
                                 CompressedEnum::size >::offset
            *
            CompressedEnum::offset *
                                 CompressedEnum::size >::size
       >
    > c1;
}
[snip]

-regards,
Larry