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java.lang.Object net.sf.saxon.expr.Expression net.sf.saxon.expr.TailExpression
public class TailExpression
A TailExpression represents a FilterExpression of the form EXPR[position() > n] Here n is usually 2, but we allow other values
Field Summary |
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Fields inherited from class net.sf.saxon.expr.Expression |
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EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD |
Constructor Summary | |
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TailExpression(Expression base,
int start)
Construct a TailExpression, representing a filter expression of the form $base[position() >= $start] |
Method Summary | |
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int |
computeCardinality()
Compute the static cardinality of this expression |
int |
computeSpecialProperties()
Compute the special properties of this expression. |
Expression |
copy()
Copy an expression. |
boolean |
equals(Object other)
Compare two expressions to see if they are equal |
void |
explain(ExpressionPresenter destination)
Diagnostic print of expression structure. |
Expression |
getBaseExpression()
Get the base expression (of which this expression returns the tail part of the value) |
ItemType |
getItemType(TypeHierarchy th)
Determine the data type of the expression, if possible. |
int |
getStart()
Get the start offset |
int |
hashCode()
|
SequenceIterator |
iterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence. |
Iterator<Expression> |
iterateSubExpressions()
Get the immediate sub-expressions of this expression. |
Expression |
optimize(ExpressionVisitor visitor,
ExpressionVisitor.ContextItemType contextItemType)
Perform optimisation of an expression and its subexpressions. |
Expression |
promote(PromotionOffer offer,
Expression parent)
Offer promotion for this subexpression. |
boolean |
replaceSubExpression(Expression original,
Expression replacement)
Replace one subexpression by a replacement subexpression |
Expression |
typeCheck(ExpressionVisitor visitor,
ExpressionVisitor.ContextItemType contextItemType)
Perform type checking of an expression and its subexpressions. |
Methods inherited from class java.lang.Object |
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clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
Constructor Detail |
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public TailExpression(Expression base, int start)
base
- the expression to be filteredstart
- the position (1-based) of the first item to be includedMethod Detail |
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public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException
Expression
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 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.
typeCheck
in class Expression
visitor
- an expression visitorcontextItemType
- 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
XPathException
- if an error is discovered during this phase
(typically a type error)public Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException
Expression
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.
optimize
in class Expression
visitor
- an expression visitorcontextItemType
- 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
XPathException
- if an error is discovered during this phase
(typically a type error)public Expression promote(PromotionOffer offer, Expression parent) throws XPathException
Expression
This method must be overridden for any Expression that has subexpressions.
promote
in class Expression
offer
- details of the offer, for example the offer to move
expressions that don't depend on the context to an outer level in
the containing expressionparent
- the containing expression in the expression tree
XPathException
- if any error is detectedpublic int computeSpecialProperties()
Expression
StaticProperty
. The "special" properties are properties
other than cardinality and dependencies, and most of them relate to properties of node sequences, for
example whether the nodes are in document order.
computeSpecialProperties
in class Expression
public Expression copy()
copy
in class Expression
public ItemType getItemType(TypeHierarchy th)
Expression
This method should always return a result, though it may be the best approximation that is available at the time.
getItemType
in class Expression
th
- the type hierarchy cache
public int computeCardinality()
Expression
computeCardinality
in class Expression
StaticProperty.ALLOWS_ZERO_OR_ONE
,
StaticProperty.EXACTLY_ONE
, StaticProperty.ALLOWS_ONE_OR_MORE
,
StaticProperty.ALLOWS_ZERO_OR_MORE
public Iterator<Expression> iterateSubExpressions()
Expression
iterateSubExpressions
in class Expression
public boolean replaceSubExpression(Expression original, Expression replacement)
replaceSubExpression
in class Expression
original
- the original subexpressionreplacement
- the replacement subexpression
public Expression getBaseExpression()
public int getStart()
public boolean equals(Object other)
equals
in class Object
other
- the other expression
public int hashCode()
hashCode
in class Object
public SequenceIterator iterate(XPathContext context) throws XPathException
Expression
iterate
in class Expression
context
- supplies the context for evaluation
XPathException
- if any dynamic error occurs evaluating the
expressionpublic void explain(ExpressionPresenter destination)
explain
in class Expression
destination
- the expression presenter used to display the structure
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