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The XSLT and XQuery Processor
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2023 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.ContextItemStaticInfo;
import net.sf.saxon.expr.parser.ExpressionVisitor;
import net.sf.saxon.expr.parser.Token;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.BuiltInAtomicType;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.value.BooleanValue;
/**
* This class implements a comparison of a computed value to a literal constant using one of the operators
* eq, ne, lt, gt, le, ge. The semantics are identical to ValueComparison, but this is a fast path for an
* important common case. Different subclasses handle different types of constant.
*/
public abstract class CompareToConstant extends UnaryExpression implements ComparisonExpression {
protected int operator;
public CompareToConstant(Expression p0) {
super(p0);
}
@Override
protected OperandRole getOperandRole() {
return OperandRole.SINGLE_ATOMIC;
}
@Override
public Expression getLhsExpression() {
return getBaseExpression();
}
@Override
public Operand getLhs() {
return getOperand();
}
@Override
public abstract Expression getRhsExpression();
@Override
public Operand getRhs() {
return new Operand(this, getRhsExpression(), OperandRole.SINGLE_ATOMIC);
}
/**
* Get the comparison operator
*
* @return one of {@link Token#FEQ}, {@link Token#FNE}, {@link Token#FGE},
* {@link Token#FGT}, {@link Token#FLE}, {@link Token#FLT}
*/
public int getComparisonOperator() {
return operator;
}
/**
* An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
* This method indicates which of these methods is provided directly. The other methods will always be available
* indirectly, using an implementation that relies on one of the other methods.
*
* @return the value {@link #EVALUATE_METHOD}
*/
@Override
public int getImplementationMethod() {
return EVALUATE_METHOD;
}
@Override
protected int computeSpecialProperties() {
return StaticProperty.NO_NODES_NEWLY_CREATED;
}
/**
* 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 net.sf.saxon.trans.XPathException
* if any dynamic error occurs evaluating the
* expression
*/
@Override
public BooleanValue evaluateItem(XPathContext context) throws XPathException {
return BooleanValue.get(effectiveBooleanValue(context));
}
/**
* Perform optimisation of an expression and its subexpressions. This is the third and final
* phase of static optimization.
* 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 the expression visitor
* @param contextInfo 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*/
@Override
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException {
getOperand().optimize(visitor, contextInfo);
if (getLhsExpression() instanceof Literal) {
return Literal.makeLiteral(BooleanValue.get(effectiveBooleanValue(null)), this);
}
return this;
}
/**
* Determine the data type of the expression, if possible. All expression return
* sequences, in general; this method determines the type of the items within the
* sequence, assuming that (a) this is known in advance, and (b) it is the same for
* all items in the sequence.
* This method should always return a result, though it may be the best approximation
* that is available at the time.
*
* @return a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER,
* Type.NODE, or Type.ITEM (meaning not known at compile time)
*/
/*@NotNull*/
@Override
public ItemType getItemType() {
return BuiltInAtomicType.BOOLEAN;
}
/**
* Get the primitive (singleton) operator used: one of Token.FEQ, Token.FNE, Token.FLT, Token.FGT,
* Token.FLE, Token.FGE
*/
@Override
public int getSingletonOperator() {
return operator;
}
/**
* Determine whether untyped atomic values should be converted to the type of the other operand
*
* @return true if untyped values should be converted to the type of the other operand, false if they
* should be converted to strings.
*/
@Override
public boolean convertsUntypedToOther() {
return true;
}
/**
* Interpret the result of the comparison
* @param operator the operator for example {@link Token#FEQ} or {@link Token#FLE}
* @param c -1, 0, or +1, depending on how the operands compare
* @return true or false depending on the operator in use
*/
public static boolean interpretComparisonResult(int operator, int c) {
switch (operator) {
case Token.FEQ:
return c == 0;
case Token.FNE:
return c != 0;
case Token.FGT:
return c > 0;
case Token.FLT:
return c < 0;
case Token.FGE:
return c >= 0;
case Token.FLE:
return c <= 0;
default:
throw new UnsupportedOperationException("Unknown operator " + operator);
}
}
}