[Boost-users] Help with (possibly MPL) pattern for a viewer that may contain a copy of statically allocated data

Subject: [Boost-users] Help with (possibly MPL) pattern for a viewer that may contain a copy of statically allocated data
From: Jesse Perla (jesseperla_at_[hidden])
Date: 2009-01-24 15:05:59

I am wondering what the best pattern/approach for a data structure that may
contain either a reference or a copy of some data used in a constructor.  I
would love the opportunity to have the data structure capable of
conditionally storing the data for the data copy on the stack.  Are there
any fancy generic tricks/patterns to do this using boost::mpl, etc.?
So to put in some pseudocode notes for discussion to get the point across of
what I think I want:

boost::array< boost::array<double, M>, N> myaxis; //creates axis in a stack
allocated data structure.
regular_grid<M, N, COPYDATA> my_grid(axis_values);
regular_grid<M, N, REFDATA> my_grid(axis_values);

template<int M, int N, int ConstructionPolicy>
class regular_grid
{
     boost::array< boost::array<double, M>, N>& axis_ref_; //Reference to
the axis, either static or actual reference.  All code in the class would
use this, not axis_

    STATIC_IF(ConstructionPolicy == COPYDATA)
     {
            boost::array< boost::array<double, M>, N> axis_;
            regular_grid(const boost::array< boost::array<double, M>, N>&
axis) : axis_(axis), axis_ref_(axis_) //constructor makes copy, sets ref to
copy.
           {
           }

     }
    STATIC_ELSE(ConstructionPolicy == REFDATA)
    {
            regular_grid(const boost::array< boost::array<double, M>, N>&
axis) : axis_ref_(axis) {} //constructor just uses the ref.
    }
};

Is this possible?  any ideas on code to look at to see how to do it?