package net.sf.saxon.sort;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.expr.*;
import net.sf.saxon.om.Item;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.ExternalObjectType;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.value.ObjectValue;
import net.sf.saxon.value.Value;
import java.util.Arrays;
import java.util.Iterator;
/**
* A tuple expression is an expression that returns a tuple. Specifically,
* it is a list of n expressions, which are evaluated to create a list of n items.
* Tuple expressions are used during the evaluation of a FLWR expression. A tuple
* is not a value within the XPath/XQuery type system, so it is represented as
* an external object, specifically as a Java array wrapped inside an ObjectValue.
*
*/
public class TupleExpression extends Expression {
Expression[] components;
int[] evaluationModes;
public TupleExpression(int width) {
components = new Expression[width];
evaluationModes = new int[width];
}
/**
* Set the i'th component expression of the tuple
* @param i identifies the component to set
* @param exp the component expression
*/
public void setExpression(int i, Expression exp) {
components[i] = exp;
adoptChildExpression(components[i]);
evaluationModes[i] = ExpressionTool.UNDECIDED;
}
/**
* Get the component expressions
* @return the component expressions, as an array
*/
public Expression[] getComponents() {
return components;
}
public Expression simplify(ExpressionVisitor visitor) throws XPathException {
for (int i=0; i<components.length; i++) {
components[i] = visitor.simplify(components[i]);
adoptChildExpression(components[i]);
}
return this;
}
public Expression promote(PromotionOffer offer) throws XPathException {
for (int i=0; i<components.length; i++) {
components[i] = doPromotion(components[i], offer);
adoptChildExpression(components[i]);
}
return this;
}
public ItemType getItemType(TypeHierarchy th) {
return new ExternalObjectType(Object.class, th.getConfiguration());
}
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
for (int i=0; i<components.length; i++) {
components[i] = visitor.typeCheck(components[i], contextItemType);
adoptChildExpression(components[i]);
}
return this;
}
/**
* Perform optimisation of an expression and its subexpressions.
* <p/>
* <p>This method is called after all references to functions and variables have been resolved
* to the declaration of the function or variable, and after all type checking has been done.</p>
*
* @param visitor an expression visitor
* @param contextItemType the static type of "." at the point where this expression is invoked.
* The parameter is set to null if it is known statically that the context item will be undefined.
* If the type of the context item is not known statically, the argument is set to
* {@link net.sf.saxon.type.Type#ITEM_TYPE}
* @return the original expression, rewritten if appropriate to optimize execution
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
for (int i=0; i<components.length; i++) {
components[i] = visitor.optimize(components[i], contextItemType);
adoptChildExpression(components[i]);
if (i < 2) {
// Although TupleExpressions could be used for many purposes, in practice they are used
// for delivering the tuples used in a FLWOR "order by" clause; the first item in the tuple
// is the return value of the FLWOR, while the others are the sort keys. The return value and
// the first sort key will always be needed, so we evaluate them eagerly. The second and subsequent
// sort keys will often not be needed, so we evaluate them lazily.
evaluationModes[i] = ExpressionTool.eagerEvaluationMode(components[i]);
} else {
evaluationModes[i] = ExpressionTool.lazyEvaluationMode(components[i]);
}
}
return this;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
public Expression copy() {
TupleExpression te = new TupleExpression(components.length);
Expression[] c2 = new Expression[components.length];
int[] e2 = new int[components.length];
for (int i=0; i<components.length; i++) {
c2[i] = components[i].copy();
e2[i] = evaluationModes[i];
}
te.components = c2;
te.evaluationModes = e2;
return te;
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*/
public void explain(ExpressionPresenter out) {
out.startElement("tuple");
for (int i=0; i<components.length; i++) {
components[i].explain(out);
}
out.endElement();
}
public Item evaluateItem(XPathContext context) throws XPathException {
Value[] tuple = new Value[components.length];
for (int i=0; i<components.length; i++) {
tuple[i] = Value.asValue(ExpressionTool.evaluate(components[i], evaluationModes[i], context, 10));
}
return new ObjectValue(tuple);
}
/**
* Get the cardinality of the expression. This is exactly one, in the sense
* that evaluating the TupleExpression returns a single tuple.
* @return the static cardinality - EXACTLY_ONE
*/
public int computeCardinality() {
return StaticProperty.EXACTLY_ONE;
}
public int getIntrinsicDependencies() {
return 0;
}
public Iterator iterateSubExpressions() {
return Arrays.asList(components).iterator();
}
/**
* 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;
for (int i=0; i<components.length; i++) {
if (components[i] == original) {
components[i] = replacement;
found = true;
}
}
return found;
}
}
//
// 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
//