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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.ExpressionTool;
import net.sf.saxon.expr.parser.ExpressionVisitor;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.BuiltInAtomicType;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.value.BooleanValue;
import net.sf.saxon.value.Cardinality;
import net.sf.saxon.value.SequenceType;
import java.util.List;
/**
* InstanceOf Expression: implements "Expr instance of data-type"
*/
public final class InstanceOfExpression extends UnaryExpression {
ItemType targetType;
int targetCardinality;
/**
* Construct an "instance of" expression in the form "source instance of target"
* @param source the expression whose type is to be tested
* @param target the type against which it is tested
*/
public InstanceOfExpression(Expression source, SequenceType target) {
super(source);
targetType = target.getPrimaryType();
if (targetType == null) {
throw new IllegalArgumentException("Primary item type must not be null");
}
targetCardinality = target.getCardinality();
}
/**
* Get the item type that we are testing for membership of
* @return the item type
*/
public ItemType getRequiredItemType() {
return targetType;
}
/**
* Get the cardinality that we are testing for membership of
* @return the required cardinality
*/
public int getRequiredCardinality() {
return targetCardinality;
}
/**
* Type-check the expression
* @return the checked expression
*/
/*@NotNull*/
public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
operand = visitor.typeCheck(operand, contextItemType);
if (operand instanceof Literal) {
Literal lit = Literal.makeLiteral(
evaluateItem(visitor.getStaticContext().makeEarlyEvaluationContext()));
ExpressionTool.copyLocationInfo(this, lit);
return lit;
}
// See if we can get the answer by static analysis.
if (Cardinality.subsumes(targetCardinality, operand.getCardinality())) {
final TypeHierarchy th = visitor.getConfiguration().getTypeHierarchy();
int relation = th.relationship(operand.getItemType(th), targetType);
if (relation == TypeHierarchy.SAME_TYPE || relation == TypeHierarchy.SUBSUMED_BY) {
Literal lit = Literal.makeLiteral(BooleanValue.TRUE);
ExpressionTool.copyLocationInfo(this, lit);
return lit;
} else if (relation == TypeHierarchy.DISJOINT) {
// if the item types are disjoint, the result might still be true if both sequences are empty
if (!Cardinality.allowsZero(targetCardinality) || !Cardinality.allowsZero(operand.getCardinality())) {
Literal lit = Literal.makeLiteral(BooleanValue.FALSE);
ExpressionTool.copyLocationInfo(this, lit);
return lit;
}
}
}
return this;
}
/**
* Perform optimisation of an expression and its subexpressions.
*
* 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.
*
* @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)
*/
/*@NotNull*/
public Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
Expression e = super.optimize(visitor, contextItemType);
if (e != this) {
return e;
}
if (Cardinality.subsumes(targetCardinality, operand.getCardinality())) {
final TypeHierarchy th = visitor.getConfiguration().getTypeHierarchy();
int relation = th.relationship(operand.getItemType(th), targetType);
if (relation == TypeHierarchy.SAME_TYPE || relation == TypeHierarchy.SUBSUMED_BY) {
return Literal.makeLiteral(BooleanValue.TRUE);
} else if (relation == TypeHierarchy.DISJOINT) {
// if the item types are disjoint, the result might still be true if both sequences are empty
if (!Cardinality.allowsZero(targetCardinality) || !Cardinality.allowsZero(operand.getCardinality())) {
return Literal.makeLiteral(BooleanValue.FALSE);
}
}
}
return this;
}
/**
* Is this expression the same as another expression?
*/
public boolean equals(Object other) {
return super.equals(other) &&
targetType == ((InstanceOfExpression)other).targetType &&
targetCardinality == ((InstanceOfExpression)other).targetCardinality;
}
/**
* get HashCode for comparing two expressions. Note that this hashcode gives the same
* result for (A op B) and for (B op A), whether or not the operator is commutative.
*/
@Override
public int hashCode() {
return super.hashCode() ^ targetType.hashCode() ^ targetCardinality;
}
/**
* Determine the cardinality
*/
public int computeCardinality() {
return StaticProperty.EXACTLY_ONE;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
/*@NotNull*/
public Expression copy() {
return new InstanceOfExpression(getBaseExpression().copy(),
SequenceType.makeSequenceType(targetType, targetCardinality));
}
/**
* Determine the data type of the result of the InstanceOf expression
* @param th the type hierarchy cache
*/
/*@NotNull*/
public ItemType getItemType(TypeHierarchy th) {
return BuiltInAtomicType.BOOLEAN;
}
/**
* Evaluate the expression
*/
public BooleanValue evaluateItem(XPathContext context) throws XPathException {
return BooleanValue.get(effectiveBooleanValue(context));
}
/**
* Evaluate the expression as a boolean
*/
public boolean effectiveBooleanValue(XPathContext context) throws XPathException {
SequenceIterator iter = operand.iterate(context);
return isInstance(iter, context);
}
private boolean isInstance(SequenceIterator iter, XPathContext context) throws XPathException {
int count = 0;
while (true) {
Item item = iter.next();
if (item == null) break;
count++;
if (!targetType.matchesItem(item, false, context.getConfiguration())) {
iter.close();
return false;
}
if (count==2 && !Cardinality.allowsMany(targetCardinality)) {
iter.close();
return false;
}
}
return !(count == 0 && ((targetCardinality & StaticProperty.ALLOWS_ZERO) == 0));
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*/
public void explain(ExpressionPresenter destination) {
destination.startElement("instance");
destination.emitAttribute("of", targetType.toString());
destination.emitAttribute("occurs", Cardinality.getOccurrenceIndicator(targetCardinality));
operand.explain(destination);
destination.endElement();
}
/**
* The toString() method for an expression attempts to give a representation of the expression
* in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
* In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
*/
@Override
public String toString() {
String occ = Cardinality.getOccurrenceIndicator(targetCardinality);
return "(" + operand.toString() + " instance of " +
targetType.toString() + occ + ")";
}
}
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