net.sf.saxon.expr
Class IsLastExpression

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

public final class IsLastExpression
extends Expression

A position() eq last() expression, generated by the optimizer.

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
IsLastExpression(boolean condition)
          Construct a condition that tests position() eq last() (if condition is true) or position() ne last() (if condition is false).
 
Method Summary
 int computeCardinality()
          Determine the static cardinality
 int computeSpecialProperties()
          Determine the special properties of this expression
 Expression copy()
          Copy an expression.
 Item evaluateItem(XPathContext c)
          Evaluate an expression as a single item.
 void explain(ExpressionPresenter destination)
          Diagnostic print of expression structure.
 boolean getCondition()
          Get the condition we are testing for
 int getIntrinsicDependencies()
          Get the dependencies of this expression on the context
 ItemType getItemType(TypeHierarchy th)
          Determine the data type of the expression
 Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Perform type checking of an expression and its subexpressions.
 
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, getImplementationMethod, getInstructionInfo, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, process, promote, replaceSubExpression, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

IsLastExpression

public IsLastExpression(boolean condition)
Construct a condition that tests position() eq last() (if condition is true) or position() ne last() (if condition is false).

Parameters:
condition - true if we are testing "equals", false for "not equals".
Method Detail

getCondition

public boolean getCondition()
Get the condition we are testing for

Returns:
true if we are testing "equals", false for "not equals".

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
Description copied from class: Expression
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.

Overrides:
typeCheck in class Expression
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

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
Description copied from class: Expression
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.

Overrides:
optimize in class Expression
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

computeSpecialProperties

public int computeSpecialProperties()
Determine the special properties of this expression

Returns:
StaticProperty.NON_CREATIVE.

evaluateItem

public Item evaluateItem(XPathContext c)
                  throws XPathException
Description copied from class: Expression
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.

Specified by:
evaluateItem in interface EvaluableItem
Overrides:
evaluateItem in class Expression
Parameters:
c - 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

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression

Specified by:
getItemType in class Expression
Parameters:
th - the type hierarchy cache
Returns:
Type.BOOLEAN

computeCardinality

public int computeCardinality()
Determine the static cardinality

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

getIntrinsicDependencies

public int getIntrinsicDependencies()
Get the dependencies of this expression on the context

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

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

explain

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

Specified by:
explain in class Expression
Parameters:
destination - the expression presenter used to display the structure


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