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An OSGi bundle for Saxon-HE
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 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.RoleLocator;
import net.sf.saxon.expr.parser.Token;
import net.sf.saxon.expr.parser.TypeChecker;
import net.sf.saxon.expr.sort.GlobalOrderComparer;
import net.sf.saxon.om.NodeInfo;
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;
/**
* IdentityComparison: a boolean expression that compares two nodes
* for equals, not-equals, greater-than or less-than based on identity and
* document ordering
*/
public final class IdentityComparison extends BinaryExpression {
private boolean generateIdEmulation = false;
// this flag is set if an "X is Y" or "X isnot Y" comparison is being used
// to emulate generate-id(X) = / != generate-id(Y). The handling of an empty
// sequence in the two cases is different.
/**
* Create an identity comparison identifying the two operands and the operator
* @param p1 the left-hand operand
* @param op the operator, as a token returned by the Tokenizer (e.g. Token.LT)
* @param p2 the right-hand operand
*/
public IdentityComparison(Expression p1, int op, Expression p2) {
super(p1, op, p2);
}
/**
* Set flag to indicate different empty-sequence behavior when emulating
* comparison of two generate-id's. This is relevant when operands evaluate
* to an empty sequence; if both are empty, the "is" operator returns (), while the
* generate-id() comparison compares two empty strings, which returns true; if one is
* empty, the "is" operator returns (), while the generate-id() comparison returns false.
* @param flag true if this function is being used to compare generate-id() output
*/
public void setGenerateIdEmulation(boolean flag) {
generateIdEmulation = flag;
}
/**
* Test the flag that indicates different empty-sequence behavior when emulating
* comparison of two generate-id's
* @return true if this function is being used to compare generate-id() output
*/
public boolean isGenerateIdEmulation() {
return generateIdEmulation;
}
/**
* Type-check the expression
*/
/*@NotNull*/
public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
operand0 = visitor.typeCheck(operand0, contextItemType);
operand1 = visitor.typeCheck(operand1, contextItemType);
if (!generateIdEmulation) {
if (Literal.isEmptySequence(operand0) || Literal.isEmptySequence(operand1)) {
return Literal.makeEmptySequence();
}
}
RoleLocator role0 = new RoleLocator(RoleLocator.BINARY_EXPR, Token.tokens[operator], 0);
//role0.setSourceLocator(this);
operand0 = TypeChecker.staticTypeCheck(
operand0, SequenceType.OPTIONAL_NODE, false, role0, visitor);
RoleLocator role1 = new RoleLocator(RoleLocator.BINARY_EXPR, Token.tokens[operator], 1);
//role1.setSourceLocator(this);
operand1 = TypeChecker.staticTypeCheck(
operand1, SequenceType.OPTIONAL_NODE, false, role1, visitor);
if (!Cardinality.allowsZero(operand0.getCardinality()) && !Cardinality.allowsZero(operand1.getCardinality())) {
generateIdEmulation = false;
// because the flag only makes a difference if one of the operands evaluates to ()
}
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 r = super.optimize(visitor, contextItemType);
if (r != this) {
if (!generateIdEmulation) {
if (Literal.isEmptySequence(operand0) || Literal.isEmptySequence(operand1)) {
return Literal.makeEmptySequence();
}
}
}
return r;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
/*@NotNull*/
public Expression copy() {
IdentityComparison ic = new IdentityComparison(operand0.copy(), operator, operand1.copy());
ic.generateIdEmulation = generateIdEmulation;
return ic;
}
/**
* Evaluate the expression
*/
/*@Nullable*/ public BooleanValue evaluateItem(XPathContext context) throws XPathException {
NodeInfo node0 = getNode(operand0, context);
if (node0==null) {
if (generateIdEmulation) {
return BooleanValue.get(getNode(operand1, context)==null);
}
return null;
}
NodeInfo node1 = getNode(operand1, context);
if (node1==null) {
if (generateIdEmulation) {
return BooleanValue.FALSE;
}
return null;
}
return BooleanValue.get(compareIdentity(node0, node1));
}
public boolean effectiveBooleanValue(XPathContext context) throws XPathException {
NodeInfo node0 = getNode(operand0, context);
if (node0==null) {
return generateIdEmulation && getNode(operand1, context) == null;
}
NodeInfo node1 = getNode(operand1, context);
return node1 != null && compareIdentity(node0, node1);
}
private boolean compareIdentity(NodeInfo node0, NodeInfo node1) {
switch (operator) {
case Token.IS:
return node0.isSameNodeInfo(node1);
case Token.PRECEDES:
return GlobalOrderComparer.getInstance().compare(node0, node1) < 0;
case Token.FOLLOWS:
return GlobalOrderComparer.getInstance().compare(node0, node1) > 0;
default:
throw new UnsupportedOperationException("Unknown node identity test");
}
}
private static NodeInfo getNode(Expression exp, XPathContext c) throws XPathException {
return (NodeInfo)exp.evaluateItem(c);
}
/**
* Determine the data type of the expression
* @return Type.BOOLEAN
* @param th the type hierarchy cache
*/
/*@NotNull*/
public ItemType getItemType(TypeHierarchy th) {
return BuiltInAtomicType.BOOLEAN;
}
}