from_to.hh

// Copyright (C) 2008, 2009, 2010 EPITA Research and Development
// Laboratory (LRDE)
//
// This file is part of Olena.
//
// Olena is free software: you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free
// Software Foundation, version 2 of the License.
//
// Olena is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Olena.  If not, see <http://www.gnu.org/licenses/>.
//
// As a special exception, you may use this file as part of a free
// software project without restriction.  Specifically, if other files
// instantiate templates or use macros or inline functions from this
// file, or you compile this file and link it with other files to produce
// an executable, this file does not by itself cause the resulting
// executable to be covered by the GNU General Public License.  This
// exception does not however invalidate any other reasons why the
// executable file might be covered by the GNU General Public License.

#ifndef MLN_CONVERT_FROM_TO_HH
# define MLN_CONVERT_FROM_TO_HH


# include <mln/convert/impl/all.hh>
# include <mln/convert/from_to.hxx>

# include <mln/metal/abort.hh>
# include <mln/metal/converts_to.hh>
# include <mln/metal/is.hh>
# include <mln/metal/is_a.hh>

# include <mln/value/cast.hh>

namespace mln
{

  // Forward declarations.
  template <typename E> struct Object;
  template <typename E> struct Value;
  template <typename E> struct Site_Set;
  template <typename E> struct Image;

  namespace convert
  {

    template <typename F, typename T>
    void
    from_to(const F& from, T& to);


# ifndef MLN_INCLUDE_ONLY

    namespace internal
    {

      // Dispatch to specific implementation.

      // Image -> Site_Set.
      template <typename I, typename S>
      inline
      void
      from_to_dispatch(const Image<I>& from, Site_Set<S>& to)
      {
        mlc_is(mln_trait_site_set_contents(S),
            mln::trait::site_set::contents::dynamic)::check();
        mln_precondition(exact(from).is_valid());
        mln::convert::impl::from_image_to_site_set(from, to);
      }


      // Site_Set -> Image.
      template <typename S, typename I>
      inline
      void
      from_to_dispatch(const Site_Set<S>& from, Image<I>& to)
      {
        mlc_converts_to(mln_site(S), mln_site(I))::check(); // FIXME: Is it too restrictive?
        mln_precondition(exact(from).is_valid());
        mln::convert::impl::from_site_set_to_image(from, to);
      }


      // Value -> Value
      template <typename F, typename T>
      inline
      void
      from_to_dispatch(const Value<F>& from, Value<T>& to)
      {
        mln::convert::impl::from_value_to_value(from, to);
      }



      // Dispatch related to convertible objects.

      // F -> T
      // if F convertible to T.
      template <typename F, typename T>
      inline
      void
      from_to_dispatch(metal::true_,
                       const Object<F>& from, Object<T>& to)
      {
        exact(to) = exact(from);
      }


      // F is NOT convertible to T.
      template <typename F, typename T>
      inline
      void
      from_to_dispatch(metal::false_,
                       const Object<F>& from, Object<T>& to)
      {
        over_load::from_to_(exact(from), exact(to));
      }



      // Default dispatch if the two arguments are objects.

      // Object -> Object
      template <typename F, typename T>
      inline
      void
      from_to_dispatch(const Object<F>& from, Object<T>& to)
      {
        typedef mlc_converts_to(F, T) F_converts_to_T; // FIXME: HERE we've got a problem with g++-2.95.
        internal::from_to_dispatch(F_converts_to_T(),
                                   exact(from), exact(to));
      }



      // Dispatch entry points.
      // Check whether arguments are an object or not.

      // Builtin -> Builtin
      template <typename F, typename T>
      inline
      void
      from_to_dispatch(metal::false_,  const F& from,
                       metal::false_,  T&       to)
      {
        over_load::from_to_(from, to);
      }


      // Object -> Builtin
      template <typename F, typename T>
      inline
      void
      from_to_dispatch(metal::true_,  const F& from,
                       metal::false_, T&       to)
      {
        over_load::from_to_(exact(from), to);
      }


      // Builtin -> Object
      template <typename F, typename T>
      inline
      void
      from_to_dispatch(metal::false_, const F& from,
                       metal::true_,  T&       to)
      {
        over_load::from_to_(from, exact(to));
      }

      // Object -> Object
      template <typename F, typename T>
      inline
      void
      from_to_dispatch(metal::true_,  const F& from,
                       metal::true_,  T&       to)
      {
        internal::from_to_dispatch(exact(from), exact(to));
      }


    } // end of namespace mln::convert::internal


    namespace over_load
    {


      // Object -> Object (F not convertible towards T)
      // No conversion exists!
      template <typename F, typename T>
      void
      from_to_(const Object<F>&, Object<T>&)
      {
        // This particular from-to is not defined!
        //
        // Either this conversion is meaningless or an overload is
        // missing.
        mlc_abort(F)::check();
      }


      // Object -> Object
      template <typename T>
      inline
      void
      from_to_(const Object<T>& from, Object<T>& to)
      {
        exact(to) = exact(from);
      }


      // Exact same type.
      template <typename T>
      inline
      void
      from_to_(const T& from, T& to)
      {
        to = from;
      }


      // Default conversion.
      template <typename F, typename T>
      inline
      void
      from_to_(const F& from, T& to)
      {
        to = mln::value::cast<T>(from);
      }


    } // end of namespace mln::convert::over_load



    // Facade

    template <typename F, typename T>
    inline
    void
    from_to(const F& from, T& to)
    {
      typedef mlc_is_a(F, Object) F_is_object;
      typedef mlc_is_a(T, Object) T_is_object;
      internal::from_to_dispatch(F_is_object(), from,
                                 T_is_object(), to);
    }


# endif // ! MLN_INCLUDE_ONLY

  } // end of namespace mln::convert

} // end of namespace mln


#endif // ! MLN_CONVERT_FROM_TO_HH