net.sf.saxon.expr.PatternMatchExpression Maven / Gradle / Ivy
package net.sf.saxon.expr;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.NodeInfo;
import net.sf.saxon.pattern.Pattern;
import net.sf.saxon.pattern.PatternSponsor;
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 java.util.Iterator;
/**
* A PatternMatchExpression is a boolean expression that returns true if and only if the context node
* matches a given pattern.
*/
public class PatternMatchExpression extends Expression {
private Pattern pattern;
/**
* Create a pattern match expression
* @param pattern the pattern to be matched
*/
public PatternMatchExpression(Pattern pattern) {
this.pattern = pattern;
}
/**
* Get the underlying pattern
* @return the pattern
*/
public Pattern getPattern() {
return pattern;
}
/**
* Get the cardinality of this expression
* @return the value @link {StaticProperty#EXACTLY_ONE}
*/
protected int computeCardinality() {
return StaticProperty.EXACTLY_ONE;
}
/**
* Perform type checking of an expression and its subexpressions. This is the second phase of
* static optimization.
*
* This checks statically that the operands of the expression have
* the correct type; if necessary it generates code to do run-time type checking or type
* conversion. A static type error is reported only if execution cannot possibly succeed, that
* is, if a run-time type error is inevitable. The call may return a modified form of the expression.
*
* This method is called after all references to functions and variables have been resolved
* to the declaration of the function or variable. However, the types of such functions and
* variables may not be accurately known if they have not been explicitly declared.
*
* If the implementation returns a value other than "this", then it is required to ensure that
* the parent pointer and location information in the returned expression have been set up correctly.
* It should not rely on the caller to do this, although for historical reasons many callers do so.
*
* @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 to perform necessary run-time type checks,
* and to perform other type-related optimizations
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
return this;
}
/**
* 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 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 {
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.
*
* @param th the type hierarchy cache
* @return a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER,
* Type.NODE, or Type.ITEM (meaning not known at compile time)
*/
public ItemType getItemType(TypeHierarchy th) {
return BuiltInAtomicType.BOOLEAN;
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*/
public void explain(ExpressionPresenter destination) {
destination.startElement("patternMatch");
destination.emitAttribute("match", pattern.toString());
destination.endElement();
}
/**
* Determine the intrinsic dependencies of an expression, that is, those which are not derived
* from the dependencies of its subexpressions. For example, position() has an intrinsic dependency
* on the context position, while (position()+1) does not. The default implementation
* of the method returns 0, indicating "no dependencies".
*
* @return a set of bit-significant flags identifying the "intrinsic"
* dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
*/
public int getIntrinsicDependencies() {
return StaticProperty.DEPENDS_ON_CONTEXT_ITEM;
}
/**
* Copy an expression. This makes a deep copy.
* @return the copy of the original expression
*/
public Expression copy() {
throw new UnsupportedOperationException("copy");
}
/**
* Get the immediate sub-expressions of this expression. Default implementation
* returns a zero-length array, appropriate for an expression that has no
* sub-expressions.
*
* @return an iterator containing the sub-expressions of this expression
*/
public Iterator iterateSubExpressions() {
return new PatternSponsor(pattern).iterateSubExpressions();
}
/**
* 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
*/
public Item evaluateItem(XPathContext context) throws XPathException {
return BooleanValue.get(effectiveBooleanValue(context));
}
/**
* Get the effective boolean value of the expression. This returns false if the value
* is the empty sequence, a zero-length string, a number equal to zero, or the boolean
* false. Otherwise it returns true.
*
* @param context The context in which the expression is to be evaluated
* @return the effective boolean value
* @throws net.sf.saxon.trans.XPathException
* if any dynamic error occurs evaluating the
* expression
*/
public boolean effectiveBooleanValue(XPathContext context) throws XPathException {
Item contextItem = context.getContextItem();
return (contextItem instanceof NodeInfo) && pattern.matches(((NodeInfo)contextItem), context);
}
}
//
// 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.
//
// Contributor(s):
//
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