code: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements. See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership. The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the  "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  /*
   * $Id$
   */
  package org.apache.xpath.operations;
  
  import org.apache.xml.dtm.DTMManager;
  import org.apache.xpath.Expression;
  import org.apache.xpath.XPathContext;
  import org.apache.xpath.objects.XNodeSet;
  import org.apache.xpath.objects.XObject;
  
  
  /**
   * This is a "smart" variable reference that is used in situations where 
   * an absolute path is optimized into a variable reference, but may 
   * be used in some situations where the document context may have changed.
   * For instance, in select="document(doc/@href)//name[//salary &gt; 7250]", the 
   * root in the predicate will be different for each node in the set.  While 
   * this is easy to detect statically in this case, in other cases static 
   * detection would be very hard or impossible.  So, this class does a dynamic check 
   * to make sure the document context of the referenced variable is the same as 
   * the current document context, and, if it is not, execute the referenced variable's 
   * expression with the current context instead.
   */
  public class VariableSafeAbsRef extends Variable
  {
      static final long serialVersionUID = -9174661990819967452L;
  	
    /**
     * Dereference the variable, and return the reference value.  Note that lazy 
     * evaluation will occur.  If a variable within scope is not found, a warning 
     * will be sent to the error listener, and an empty nodeset will be returned.
     *
     *
     * @param xctxt The runtime execution context.
     *
     * @return The evaluated variable, or an empty nodeset if not found.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public XObject execute(XPathContext xctxt, boolean destructiveOK) 
    	throws javax.xml.transform.TransformerException
    {
    	XNodeSet xns = (XNodeSet)super.execute(xctxt, destructiveOK);
    	DTMManager dtmMgr = xctxt.getDTMManager();
    	int context = xctxt.getContextNode();
    	if(dtmMgr.getDTM(xns.getRoot()).getDocument() != 
    	   dtmMgr.getDTM(context).getDocument())
    	{
    		Expression expr = (Expression)xns.getContainedIter();
    		xns = (XNodeSet)expr.asIterator(xctxt, context);
    	}
    	return xns;
    }
  
  }
  
  