net.sf.saxon.expr.TailExpression Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of saxon9 Show documentation
Provides a basic XSLT 2.0 and XQuery 1.0 processor (W3C Recommendations, January 2007). Command line interfaces and implementations of several Java APIs (DOM, XPath, s9api) are also included.
The newest version!
package net.sf.saxon.expr;

import net.sf.saxon.om.*;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.trace.ExpressionPresenter;

import java.util.Iterator;

/**
 * A TailExpression represents a FilterExpression of the form EXPR[position() > n]
 * Here n is usually 2, but we allow other values
 */
public class TailExpression extends Expression {

    Expression base;
    int start;      // 1-based offset of first item from base expression
                    // to be included

    /**
     * Construct a TailExpression, representing a filter expression of the form
     * $base[position() >= $start]
     * @param base    the expression to be filtered
     * @param start   the position (1-based) of the first item to be included
     */

    public TailExpression(Expression base, int start) {
        this.base = base;
        this.start = start;
        adoptChildExpression(base);
    }

    public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
        base = visitor.typeCheck(base, contextItemType);
        return this;
    }

    public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
        base = visitor.optimize(base, contextItemType);
        return this;
    }

    public Expression promote(PromotionOffer offer) throws XPathException {
        Expression exp = offer.accept(this);
        if (exp != null) {
            return exp;
        } else {
            if (offer.action != PromotionOffer.UNORDERED) {
                base = doPromotion(base, offer);
            }
            return this;
        }
    }

    public int computeSpecialProperties() {
        return base.getSpecialProperties();
    }

    /**
     * Copy an expression. This makes a deep copy.
     *
     * @return the copy of the original expression
     */

    public Expression copy() {
        return new TailExpression(base.copy(), start);
    }

    public ItemType getItemType(TypeHierarchy th) {
        return base.getItemType(th);
    }

    public int computeCardinality() {
        return base.getCardinality() | StaticProperty.ALLOWS_ZERO;
    }

    public Iterator iterateSubExpressions() {
        return new MonoIterator(base);
    }

    /**
      * Replace one subexpression by a replacement subexpression
      * @param original the original subexpression
      * @param replacement the replacement subexpression
      * @return true if the original subexpression is found
      */

     public boolean replaceSubExpression(Expression original, Expression replacement) {
         boolean found = false;
         if (base == original) {
             base = replacement;
             found = true;
         }
         return found;
     }

    /**
     * Get the base expression (of which this expression returns the tail part of the value)
     * @return the base expression
     */

    public Expression getBaseExpression() {
        return base;
    }

    /**
     * Get the start offset
     * @return the one-based start offset (returns 2 if all but the first item is being selected)
     */

    public int getStart() {
        return start;
    }

    /**
     * Compare two expressions to see if they are equal
     * @param other the other expression
     * @return true if the expressions are equivalent
     */

    public boolean equals(Object other) {
        return other instanceof TailExpression &&
                base.equals(((TailExpression)other).base) &&
                start == ((TailExpression)other).start;
    }

    public int hashCode() {
        return base.hashCode();
    }

    public SequenceIterator iterate(XPathContext context) throws XPathException {
        SequenceIterator baseIter = base.iterate(context);
        if ((baseIter.getProperties() & SequenceIterator.GROUNDED) != 0) {
            return new ValueTailIterator(((GroundedIterator)baseIter).materialize(), start - 1);
        } else {
            return TailIterator.make(baseIter, start);
        }
    }

    /**
     * Diagnostic print of expression structure. The abstract expression tree
     * is written to the supplied output destination.
     */

    public void explain(ExpressionPresenter destination) {
        destination.startElement("tail");
        destination.emitAttribute("start", start+"");
        base.explain(destination);
        destination.endElement();
    }

}

//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (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.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file.
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none.
//