net.sf.saxon.expr
Class CardinalityChecker

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.UnaryExpression
          extended by net.sf.saxon.expr.CardinalityChecker
All Implemented Interfaces:
Serializable, SourceLocator, EvaluableItem, SequenceIterable, InstructionInfoProvider

public final class CardinalityChecker
extends UnaryExpression

A CardinalityChecker implements the cardinality checking of "treat as": that is, it returns the supplied sequence, checking that its cardinality is correct

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Method Summary
 int computeCardinality()
          Determine the static cardinality of the expression
 int computeSpecialProperties()
          Get the static properties of this expression (other than its type).
 Expression copy()
          Copy an expression.
static String depictSequenceStart(SequenceIterator seq, int max)
          Show the first couple of items in a sequence in an error message
 boolean equals(Object other)
          Is this expression the same as another expression?
 Item evaluateItem(XPathContext context)
          Evaluate as an Item.
 void explain(ExpressionPresenter out)
          Diagnostic print of expression structure.
 int getImplementationMethod()
          An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
 ItemType getItemType(TypeHierarchy th)
          Determine the data type of the items returned by the expression, if possible
 int getRequiredCardinality()
          Get the required cardinality
 RoleLocator getRoleLocator()
          Get the RoleLocator, which contains diagnostic information for use if the cardinality check fails
 SequenceIterator iterate(XPathContext context)
          Iterate over the sequence of values
static Expression makeCardinalityChecker(Expression sequence, int cardinality, RoleLocator role)
          Factory method to construct a CardinalityChecker.
 Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 void process(XPathContext context)
          Process the instruction, without returning any tail calls
 void setErrorCode(String code)
          Set the error code to be returned (this is used when evaluating the functions such as exactly-one() which have their own error codes)
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Type-check the expression
 
Methods inherited from class net.sf.saxon.expr.UnaryExpression
getBaseExpression, hashCode, iterateSubExpressions, promote, replaceSubExpression, simplify, toString
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, effectiveBooleanValue, evaluateAsString, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterateEvents, markTailFunctionCalls, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Method Detail

makeCardinalityChecker

public static Expression makeCardinalityChecker(Expression sequence,
                                                int cardinality,
                                                RoleLocator role)
Factory method to construct a CardinalityChecker. The method may create an expression that combines the cardinality checking with the functionality of the underlying expression class

Parameters:
sequence - the base sequence whose cardinality is to be checked
cardinality - the required cardinality
role - information to be used in error reporting
Returns:
a new Expression that does the CardinalityChecking (not necessarily a CardinalityChecker)

getRequiredCardinality

public int getRequiredCardinality()
Get the required cardinality

Returns:
the cardinality required by this checker

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException
Type-check the expression

Overrides:
typeCheck in class UnaryExpression
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 Type.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)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
                    throws XPathException
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.

Overrides:
optimize in class UnaryExpression
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 Type.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)

setErrorCode

public void setErrorCode(String code)
Set the error code to be returned (this is used when evaluating the functions such as exactly-one() which have their own error codes)

Parameters:
code - the error code to be used

getRoleLocator

public RoleLocator getRoleLocator()
Get the RoleLocator, which contains diagnostic information for use if the cardinality check fails

Returns:
the diagnostic information

getImplementationMethod

public int getImplementationMethod()
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. This implementation provides both iterate() and process() methods natively.

Overrides:
getImplementationMethod in class Expression
Returns:
the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Iterate over the sequence of values

Specified by:
iterate in interface SequenceIterable
Overrides:
iterate in class Expression
Parameters:
context - supplies the context for evaluation
Returns:
a SequenceIterator that can be used to iterate over the result of the expression
Throws:
XPathException - if any dynamic error occurs evaluating the expression

depictSequenceStart

public static String depictSequenceStart(SequenceIterator seq,
                                         int max)
Show the first couple of items in a sequence in an error message

Parameters:
seq - iterator over the sequence
max - maximum number of items to be shown
Returns:
a message display of the contents of the sequence

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Evaluate as an Item.

Specified by:
evaluateItem in interface EvaluableItem
Overrides:
evaluateItem in class Expression
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:
XPathException - if any dynamic error occurs evaluating the expression

process

public void process(XPathContext context)
             throws XPathException
Process the instruction, without returning any tail calls

Overrides:
process in class Expression
Parameters:
context - The dynamic context, giving access to the current node, the current variables, etc.
Throws:
XPathException

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible

Overrides:
getItemType in class UnaryExpression
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 in advance)

computeCardinality

public int computeCardinality()
Determine the static cardinality of the expression

Overrides:
computeCardinality in class UnaryExpression
Returns:
the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE

computeSpecialProperties

public int computeSpecialProperties()
Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Overrides:
computeSpecialProperties in class UnaryExpression
Returns:
the special properties, as a bit-significant integer

copy

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

Specified by:
copy in class Expression
Returns:
the copy of the original expression

equals

public boolean equals(Object other)
Is this expression the same as another expression?

Overrides:
equals in class UnaryExpression

explain

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

Overrides:
explain in class UnaryExpression
Parameters:
out - the expression presenter used to display the structure


Copyright (C) Michael H. Kay. All rights reserved.