/*
// $Id: //open/dev/farrago/src/org/eigenbase/rel/RelVisitor.java#10 $
// Package org.eigenbase is a class library of data management components.
// Copyright (C) 2005-2009 The Eigenbase Project
// Copyright (C) 2002-2009 SQLstream, Inc.
// Copyright (C) 2005-2009 LucidEra, Inc.
// Portions Copyright (C) 2003-2009 John V. Sichi
//
// This program 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; either version 2 of the License, or (at your option)
// any later version approved by The Eigenbase Project.
//
// This program 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
*/
package org.eigenbase.rel;

/**
 * A <code>RelVisitor</code> is a Visitor role in the {@link
 * org.eigenbase.util.Glossary#VisitorPattern visitor pattern} and visits {@link
 * RelNode} objects as the role of Element. Other components in the pattern:
 * {@link RelNode#childrenAccept(RelVisitor)}.
 *
 * @author jhyde
 * @version $Id: //open/dev/farrago/src/org/eigenbase/rel/RelVisitor.java#10 $
 * @since 22 September, 2001
 */
public abstract class RelVisitor
{
    //~ Instance fields --------------------------------------------------------

    private RelNode root;

    //~ Methods ----------------------------------------------------------------

    /**
     * Visits a node during a traversal.
     *
     * @param node Node to visit
     * @param ordinal Ordinal of node within its parent
     * @param parent Parent of the node, or null if it is the root of the
     * traversal
     */
    public void visit(
        RelNode node,
        int ordinal,
        RelNode parent)
    {
        node.childrenAccept(this);
    }

    /**
     * Replaces the root node of this traversal.
     *
     * @param node The new root node
     */
    public void replaceRoot(RelNode node)
    {
        this.root = node;
    }

    /**
     * Starts an iteration.
     */
    public RelNode go(RelNode p)
    {
        this.root = p;
        visit(p, 0, null);
        return root;
    }
}

// End RelVisitor.java
