visitor_cast.hh

/* vim: set sw=4 sts=4 et foldmethod=syntax : */
 
/*
 * Copyright (c) 2008, 2009, 2010, 2011 Ciaran McCreesh
 *
 * This file is part of the Paludis package manager. Paludis 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.
 *
 * Paludis 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 program; if not, write to the Free Software Foundation, Inc., 59 Temple
 * Place, Suite 330, Boston, MA  02111-1307  USA
 */
 
#ifndef PALUDIS_GUARD_PALUDIS_UTIL_VISITOR_CAST_HH
#define PALUDIS_GUARD_PALUDIS_UTIL_VISITOR_CAST_HH 1
 
#include <paludis/util/visitor_cast-fwd.hh>
#include <paludis/util/visitor.hh>
#include <type_traits>
 
namespace paludis
{
    template <typename To_, typename From_>
    struct VisitorCaster
    {
        To_ * visit(To_ & t)
        {
            return &t;
        }
 
        To_ * visit(From_ &)
        {
            return 0;
        }
    };
 
    template <typename C_, typename T_>
    struct CopyConst
    {
        typedef T_ Type;
    };
 
    template <typename C_, typename T_>
    struct CopyConst<const C_, T_>
    {
        typedef const T_ Type;
    };
 
    template <typename To_, typename From_, typename>
    To_ *
    visitor_cast(From_ & from)
    {
        VisitorCaster<To_, typename CopyConst<From_, typename From_::VisitableBaseClass>::Type> q;
        return from.template accept_returning<To_ *>(q);
    }
}
 
#endif