net.sf.saxon.expr

Class PatternMatchExpression

public class PatternMatchExpression extends Expression

A PatternMatchExpression is a boolean expression that returns true if and only if the context node matches a given pattern.
Constructor Summary
PatternMatchExpression(Pattern pattern)
Create a pattern match expression
Method Summary
protected intcomputeCardinality()
Get the cardinality of this expression
Expressioncopy()
Copy an expression.
booleaneffectiveBooleanValue(XPathContext context)
Get the effective boolean value of the expression.
ItemevaluateItem(XPathContext context)
Evaluate an expression as a single item.
voidexplain(ExpressionPresenter destination)
Diagnostic print of expression structure.
intgetIntrinsicDependencies()
Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the expression, if possible.
PatterngetPattern()
Get the underlying pattern
Iterator<Expression>iterateSubExpressions()
Get the immediate sub-expressions of this expression.
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Perform type checking of an expression and its subexpressions.

Constructor Detail

PatternMatchExpression

public PatternMatchExpression(Pattern pattern)
Create a pattern match expression

Parameters: pattern the pattern to be matched

Method Detail

computeCardinality

protected int computeCardinality()
Get the cardinality of this expression

Returns: the value @link {StaticProperty#EXACTLY_ONE}

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Returns: the copy of the original expression

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext 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.

Parameters: context The context in which the expression is to be evaluated

Returns: the effective boolean value

Throws: net.sf.saxon.trans.XPathException if any dynamic error occurs evaluating the expression

evaluateItem

public Item evaluateItem(XPathContext context)
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.

Parameters: context The context in which the expression is to be evaluated

Returns: 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

explain

public void explain(ExpressionPresenter destination)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

getIntrinsicDependencies

public int getIntrinsicDependencies()
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".

Returns: a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

getItemType

public ItemType getItemType(TypeHierarchy th)
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.

Parameters: th the type hierarchy cache

Returns: a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

getPattern

public Pattern getPattern()
Get the underlying pattern

Returns: the pattern

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Returns: an iterator containing the sub-expressions of this expression

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
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.

Parameters: visitor an expression visitor 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 ITEM_TYPE

Returns: the original expression, rewritten if appropriate to optimize execution

Throws: XPathException if an error is discovered during this phase (typically a type error)

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
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.

Parameters: visitor an expression visitor 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 ITEM_TYPE

Returns: 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)