[Boost-users] [mpl] Sorting types by index

26 Mar 2008

      I have an mpl::vector of all possible types I care about.  It's called AllTypes. 
    Given a sequence containing some subset of types in AllTypes, I want to 
order the sequence so that the types occur in the same relative order as in 
AllTypes.    So if AllTypes is

   A, B, C, D, E

and I'm given

   B, E, A

I want to produce

   A, B, E

Fundamentally, I'm sorting things based on their index in AllTypes.  Well, 
that's what I want to be doing.  What I'm really doing is getting compilation 
errors referring to a missing tag in my metafunction, which is called IndexOf. 
The code I'm using is below.  I'd appreciate it if people would take a look and 
help me figure out why it's not working.

Thanks,

Scott

#include 
#include 
#include 

using namespace boost;

// return the index of type T in sequence S
template
struct IndexOf {
   enum { value = mpl::distance::type
                               >::value };
};

int main()
{
   using mpl::_1;
   using mpl::_2;

   typedef mpl::vector AllTypes;

   typedef mpl::vector Unsorted;

   typedef mpl::sort,      // sort doesn't
                               IndexOf >     // compile
                    >::type
           Sorted;
}

[Boost-users] [mpl] Sorting types by index

Scott Meyers