global_ops_traits.hh

// Copyright (C) 2001, 2002, 2003  EPITA Research and Development Laboratory
//
// This file is part of the Olena Library.  This library is free
// software; you can redistribute it and/or modify it under the terms
// of the GNU General Public License version 2 as published by the
// Free Software Foundation.
//
// This library 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 this library; see the file COPYING.  If not, write to
// the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
// MA 02111-1307, USA.
//
// As a special exception, you may use this file as part of a free
// software library without restriction.  Specifically, if other files
// instantiate templates or use macros or inline functions from this
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// Public License.

#ifndef NTG_CORE_INTERNAL_GLOBAL_OPS_TRAITS_HH
# define NTG_CORE_INTERNAL_GLOBAL_OPS_TRAITS_HH

/*
  Tools to determine return type of operators given the parameters
  types. For each type, one has to specialize the traits
  operator_xxx, and then use deduce_from_traits<operator_xxx, T1, T2>
  as return type for operatorxxx(T1, T2) functions.
*/

# include <ntg/core/macros.hh>
# include <ntg/core/type_traits.hh>

# include <mlc/bool.hh>

namespace ntg {

  namespace internal {

    /*-----------.
    | Meta tools |
    `-----------*/

    struct undefined_traits {};

    template <class T>
    struct meta_undefined_traits
    {
      typedef undefined_traits ret;
      typedef undefined_traits lhs_type;
      typedef undefined_traits rhs_type;
      typedef undefined_traits traits_lhs_type;
      typedef undefined_traits traits_rhs_type;
    };

    template <class T>
    struct is_defined { enum { ret = true }; };
    template <>
    struct is_defined<undefined_traits> { enum { ret = false }; };

    /*
      get_order, get_order_inv

      These structs are used to inverse input types (if the operator
      is commutative) and to specify whether input types should be
      converted into another type (eg. the corresponding ntg_type).
    */

    template <class T1, class T2>
    struct get_order
    {
      typedef T1 traits_lhs_type;
      typedef T2 traits_rhs_type;

      typedef T1 lhs_type;
      typedef T2 rhs_type;
    };

    template <class T1, class T2>
    struct get_order_inv
    {
      typedef T2 traits_lhs_type;
      typedef T1 traits_rhs_type;

      typedef T1 lhs_type;
      typedef T2 rhs_type;
    };

    /*---------------------------.
    | Operator traits definition |
    `---------------------------*/

    template <class Op, class T, class U>
    struct operator_traits
    {
      enum { commutative = false };
      typedef undefined_traits ret;
      typedef undefined_traits impl;
    };

    struct operator_plus {};
    struct operator_minus {};
    struct operator_times {};
    struct operator_div {};
    struct operator_mod {};
    struct operator_logical {};
    struct operator_cmp {};
    struct operator_min {};
    struct operator_max {};

    /*-----------------------------------.
    | deduce_from_traits<operator, T, U> |
    `-----------------------------------*/

    template <class Op, class T, class U>
    struct deduce_from_traits
    {
    private:
      typedef ntg_type(T) T1;
      typedef ntg_type(U) T2;

      typedef typename operator_traits<Op, T1, T2>::ret traits;
      typedef typename operator_traits<Op, T2, T1>::ret rev_traits;

      enum { can_invert = (operator_traits<Op, T2, T1>::commutative
                           && is_defined<rev_traits>::ret) };

      typedef typename
      mlc::if_<is_defined<traits>::ret,
                get_order<T1, T2>, typename
                mlc::if_<can_invert,
                         get_order_inv<T1, T2>,
                         meta_undefined_traits<undefined_traits>
                        >::ret
              >::ret deduced_type;

      typedef typename deduced_type::traits_lhs_type traits_lhs_type;
      typedef typename deduced_type::traits_rhs_type traits_rhs_type;

    public:
      typedef operator_traits<Op,
                              traits_lhs_type,
                              traits_rhs_type> deduced_traits;

      typedef typename deduced_type::lhs_type lhs_type;
      typedef typename deduced_type::rhs_type rhs_type;
      typedef typename deduced_traits::ret ret;
      typedef typename deduced_traits::impl impl;
    };

  } // end of internal.

} // end of ntg.

#endif // !NTG_CORE_INTERNAL_GLOBAL_OPS_TRAITS_HH

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