net.sf.saxon.expr

Class CardinalityChecker

public final class CardinalityChecker extends UnaryExpression implements MappingExpression

A CardinalityChecker implements the cardinality checking of "treat as": that is, it returns the supplied sequence, checking that its cardinality is correct
Method Summary
intcomputeCardinality()
Determine the static cardinality of the expression
intcomputeSpecialProperties()
Get the static properties of this expression (other than its type).
Expressioncopy()
Copy an expression.
static StringdepictSequenceStart(SequenceIterator seq, int max)
Show the first couple of items in a sequence in an error message
booleanequals(Object other)
Is this expression the same as another expression?
ItemevaluateItem(XPathContext context)
Evaluate as an Item.
voidexplain(ExpressionPresenter out)
Diagnostic print of expression structure.
intgetImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible
SequenceIteratorgetMappingIterator(SequenceIterator base, XPathContext context)
intgetRequiredCardinality()
Get the required cardinality
RoleLocatorgetRoleLocator()
Get the RoleLocator, which contains diagnostic information for use if the cardinality check fails
SequenceIteratoriterate(XPathContext context)
Iterate over the sequence of values
static ExpressionmakeCardinalityChecker(Expression sequence, int cardinality, RoleLocator role)
Factory method to construct a CardinalityChecker.
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
voidprocess(XPathContext context)
Process the instruction, without returning any tail calls
voidsetErrorCode(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)
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

Method Detail

computeCardinality

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

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.

copy

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

Returns: the copy of the original 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

equals

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

evaluateItem

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

explain

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

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.

getItemType

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

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)

getMappingIterator

public SequenceIterator getMappingIterator(SequenceIterator base, XPathContext context)

getRequiredCardinality

public int getRequiredCardinality()
Get the required cardinality

Returns: the cardinality required by this checker

getRoleLocator

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

Returns: the diagnostic information

iterate

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

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)

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
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.

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)

process

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

Parameters: context The dynamic context, giving access to the current node, the current variables, etc.

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

typeCheck

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