net.sf.saxon.expr
Class TailExpression

java.lang.Object
  extended bynet.sf.saxon.expr.ComputedExpression
      extended bynet.sf.saxon.expr.TailExpression
All Implemented Interfaces:
Expression, Serializable

public class TailExpression
extends ComputedExpression

A TailExpression represents a FilterExpression of the form EXPR[position() > n] Here n is usually 2, but we allow other values

See Also:
Serialized Form

Nested Class Summary
static class TailExpression.TailIterator
           
 
Field Summary
(package private)  Expression base
           
(package private)  int start
           
 
Fields inherited from class net.sf.saxon.expr.ComputedExpression
lineNumber, NO_ARGUMENTS, staticProperties
 
Constructor Summary
TailExpression(Expression base, int start)
          Construct a TailExpression, representing a filter expression of the form $base[position() >= $start]
 
Method Summary
 Expression analyze(StaticContext env)
          Perform static analysis of an expression and its subexpressions.
 int computeCardinality()
           
 int computeSpecialProperties()
           
 void display(int level, NamePool pool)
          Diagnostic print of expression structure.
 boolean equals(Object other)
           
 Expression getBaseExpression()
           
 ItemType getItemType()
          Determine the data type of the expression, if possible.
 int getStart()
           
 Expression[] getSubExpressions()
          Get the immediate sub-expressions of this expression.
 int hashCode()
           
 SequenceIterator iterate(XPathContext context)
          Return an Iterator to iterate over the values of a sequence.
 Expression promote(PromotionOffer offer)
          Offer promotion for this subexpression.
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
computeDependencies, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getDependencies, getIntrinsicDependencies, getLineNumber, getSpecialProperties, markTailFunctionCalls, setLineNumber, simplify, typeError
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

base

Expression base

start

int start
Constructor Detail

TailExpression

public TailExpression(Expression base,
                      int start)
Construct a TailExpression, representing a filter expression of the form $base[position() >= $start]

Parameters:
base - the expression to be filtered
start - the position (1-based) of the first item to be included
Method Detail

analyze

public Expression analyze(StaticContext env)
Description copied from interface: Expression
Perform static analysis of an expression and its subexpressions.

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 will only be accurately known if they have been explicitly declared.

Parameters:
env - the static context of the expression
Returns:
the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException
Description copied from class: ComputedExpression
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.

Specified by:
promote in interface Expression
Overrides:
promote in class ComputedExpression
Parameters:
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 expression
Returns:
if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
Throws:
XPathException - if any error is detected

computeSpecialProperties

public int computeSpecialProperties()
Overrides:
computeSpecialProperties in class ComputedExpression

getItemType

public ItemType getItemType()
Description copied from interface: Expression
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.

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

computeCardinality

public int computeCardinality()
Specified by:
computeCardinality in class ComputedExpression

getSubExpressions

public Expression[] getSubExpressions()
Description copied from class: ComputedExpression
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Specified by:
getSubExpressions in interface Expression
Overrides:
getSubExpressions in class ComputedExpression
Returns:
an array containing the sub-expressions of this expression

getBaseExpression

public Expression getBaseExpression()

getStart

public int getStart()

equals

public boolean equals(Object other)

hashCode

public int hashCode()

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Description copied from class: ComputedExpression
Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Specified by:
iterate in interface Expression
Overrides:
iterate in class ComputedExpression
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

display

public void display(int level,
                    NamePool pool)
Description copied from interface: Expression
Diagnostic print of expression structure. The expression is written to the System.err output stream

Parameters:
level - indentation level for this expression