net.sf.saxon.expr.SimpleExpression Maven / Gradle / Ivy
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// Copyright (c) 2013 Saxonica Limited.
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.expr;
import net.sf.saxon.expr.parser.ExpressionVisitor;
import net.sf.saxon.expr.parser.PromotionOffer;
import net.sf.saxon.om.*;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.Type;
import net.sf.saxon.type.TypeHierarchy;
import java.util.Arrays;
import java.util.Iterator;
/**
* An abstract implementation of Expression designed to make it easy to implement new expressions,
* in particular, expressions to support extension instructions.
*
* An implementation of this class must supply the {@link Callable#call(XPathContext, net.sf.saxon.om.Sequence[])}
* method to evaluate the expression and return its result.
*/
public abstract class SimpleExpression extends Expression implements Callable {
public static final Expression[] NO_ARGUMENTS = new Expression[0];
protected Expression[] arguments = NO_ARGUMENTS;
/**
* Constructor
*/
public SimpleExpression() {
}
/**
* Set the immediate sub-expressions of this expression.
*
* @param sub an array containing the sub-expressions of this expression
*/
public void setArguments(Expression[] sub) {
arguments = sub;
for (Expression aSub : sub) {
adoptChildExpression(aSub);
}
}
/**
* Get the immediate sub-expressions of this expression.
*
* @return an array containing the sub-expressions of this expression
*/
/*@NotNull*/
public Iterator iterateSubExpressions() {
return Arrays.asList(arguments).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 < arguments.length; i++) {
if (arguments[i] == original) {
arguments[i] = replacement;
found = true;
}
}
return found;
}
/**
* Simplify the expression
*
* @param visitor an expression visitor
* @return the simplified expression
*/
/*@NotNull*/
public Expression simplify(ExpressionVisitor visitor) throws XPathException {
for (int i = 0; i < arguments.length; i++) {
if (arguments[i] != null) {
arguments[i] = visitor.simplify(arguments[i]);
}
}
return this;
}
/*@NotNull*/
public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
for (int i = 0; i < arguments.length; i++) {
if (arguments[i] != null) {
arguments[i] = visitor.typeCheck(arguments[i], contextItemType);
}
}
return this;
}
/*@NotNull*/
public Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
for (int i = 0; i < arguments.length; i++) {
if (arguments[i] != null) {
arguments[i] = visitor.optimize(arguments[i], contextItemType);
}
}
return this;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
/*@NotNull*/
public Expression copy() {
throw new UnsupportedOperationException("SimpleExpression.copy()");
}
/**
* Offer promotion for this subexpression. The offer will be accepted if the subexpression
* is not dependent on the factors (e.g. the context item) identified in the PromotionOffer.
* By default the offer is not accepted - this is appropriate in the case of simple expressions
* such as constant values and variable references where promotion would give no performance
* advantage. This method is always called at compile time.
*
* @param offer details of the offer, for example the offer to move
* expressions that don't depend on the context to an outer level in
* the containing expression
* @param parent the parent of this expression
* @return if the offer is not accepted, return this expression unchanged.
* Otherwise return the result of rewriting the expression to promote
* this subexpression
* @throws XPathException if any error is detected
*/
public Expression promote(PromotionOffer offer, Expression parent) throws XPathException {
for (int i = 0; i < arguments.length; i++) {
if (arguments[i] != null) {
arguments[i] = doPromotion(arguments[i], offer);
}
}
return this;
}
/**
* Determine the data type of the items returned by this expression. This implementation
* returns "item()", which can be overridden in a subclass.
*
* @param th the type hierarchy cache
* @return the data type
*/
/*@NotNull*/
public ItemType getItemType(TypeHierarchy th) {
return Type.ITEM_TYPE;
}
/**
* Determine the static cardinality of the expression. This implementation
* returns "zero or more", which can be overridden in a subclass.
*/
public int computeCardinality() {
if ((getImplementationMethod() & Expression.EVALUATE_METHOD) == 0) {
return StaticProperty.ALLOWS_ONE_OR_MORE;
} else {
return StaticProperty.ALLOWS_ZERO_OR_ONE;
}
}
/**
* Compute the dependencies of an expression, as the union of the
* dependencies of its subexpressions. (This is overridden for path expressions
* and filter expressions, where the dependencies of a subexpression are not all
* propogated). This method should be called only once, to compute the dependencies;
* after that, getDependencies should be used.
*
* @return the depencies, as a bit-mask
*/
public int computeDependencies() {
return super.computeDependencies();
}
/**
* Evaluate an expression as a single item. This always returns either a single Item or
* null (denoting the empty sequence). No conversion is done. This method should not be
* used unless the static type of the expression is a subtype of "item" or "item?": that is,
* it should not be called if the expression may return a sequence. There is no guarantee that
* this condition will be detected.
*
* @param context The context in which the expression is to be evaluated
* @return the node or atomic value that results from evaluating the
* expression; or null to indicate that the result is an empty
* sequence
* @throws XPathException if any dynamic error occurs evaluating the
* expression
*/
public final Item evaluateItem(XPathContext context) throws XPathException {
return call(context, evaluateArguments(context)).head();
}
/**
* Return an Iterator to iterate over the values of a sequence. The value of every
* expression can be regarded as a sequence, so this method is supported for all
* expressions. This default implementation handles iteration for expressions that
* return singleton values: for non-singleton expressions, the subclass must
* provide its own implementation.
*
* @param context supplies the context for evaluation
* @return a SequenceIterator that can be used to iterate over the result
* of the expression
* @throws XPathException if any dynamic error occurs evaluating the
* expression
*/
/*@NotNull*/
public final SequenceIterator iterate(XPathContext context) throws XPathException {
return call(context, evaluateArguments(context)).iterate();
}
/**
* Process the instruction, without returning any tail calls
*
* @param context The dynamic context, giving access to the current node,
* the current variables, etc.
*/
public final void process(XPathContext context) throws XPathException {
SequenceIterator iter = call(context, evaluateArguments(context)).iterate();
Item it;
while ((it = iter.next()) != null) {
context.getReceiver().append(it, locationId, NodeInfo.ALL_NAMESPACES);
}
}
/**
* Internal method to evaluate the arguments prior to calling the generic call() method
* @param context the XPath dynamic context
* @return the values of the (evaluated) arguments
* @throws XPathException if a dynamic error occurs
*/
private Sequence[] evaluateArguments(XPathContext context) throws XPathException {
Sequence[] iters = new Sequence[arguments.length];
for (int i = 0; i < arguments.length; i++) {
iters[i] = SequenceTool.toLazySequence(arguments[i].iterate(context));
}
return iters;
}
/**
* Get the subexpressions (arguments to this expression)
*
* @return the arguments, as an array
*/
public Expression[] getArguments() {
return arguments;
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*/
public void explain(ExpressionPresenter destination) {
destination.startElement("userExpression");
destination.emitAttribute("class", getExpressionType());
for (Expression argument : arguments) {
argument.explain(destination);
}
destination.endElement();
}
/**
* Return a distinguishing name for the expression, for use in diagnostics.
* By default the class name is used.
*
* @return a distinguishing name for the expression (defaults to the name of the implementation class)
*/
public String getExpressionType() {
return getClass().getName();
}
}
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