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

Subject: Re: [Boost-users] Help with (possibly MPL) pattern for a viewer that may contain a copy of statically allocated data
From: jesseperla (jesseperla_at_[hidden])
Date: 2009-01-29 12:15:32

On Jan 24, 3:19 pm, Steven Watanabe <watanab..._at_[hidden]> wrote:
> template<int M, int N, class Storage = boost::mpl::identity<> >
> class regular_grid {
>     typedef boost::array< boost::array<double, M>, N > array_type;
>     typedef typename boost::mpl::apply<Storage, array_type>::type
> storage_type;
>     storage_type axis_;
>     // use axis
>
> };
> typedef boost::add_reference<boost::add_const<boost::mpl::_1> >
> reference_policy;
> typedef boost::mpl::identity<> copy_policy;
>
> regular_grid<2, 3,  reference_policy> g;
> In Christ,
> Steven Watanabe

A followup if anyone else is using this code:

Steven:  Your code worked beautifully, but it turned out that I also
needed an assignment operator (which fails due to the const on the
ref).  For now, I did the following:
typedef boost::add_reference<boost::add_const<boost::mpl::_1> > >
const_reference_policy;
typedef boost::add_reference<<boost::mpl::_1 > > reference_policy;

Things *kind of* work now for the default assignment operator
generated by the compiler.  I can now create a new item and then use
the copy assignment(if they have the same storage policy).  Things
like...
  regular_grid <2,3> interp( f_values); //The default is the new non-
const reference_policy.
  regular_grid <2,3> interp3 = interp; //Works!  Also works for the
copy_policy
  interp3 = interp; //Fails!  Also fails for the copy_policy

Lower priority for me, but assignment will only work for 2 grids of
type ref or 2 of type value.  What is the best way to write the
assignment operator to allow assignment between the different policy
types? (combinations except assignment to a const_reference_policy of
course)

(my apologies for misspelling your name previously)
Thanks,
Jesse