net.sf.saxon.expr

Class SimpleMappingExpression

Implemented Interfaces:
ContextMappingFunction, EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator

public final class SimpleMappingExpression
extends Expression
implements ContextMappingFunction

A simple mapping expression is an expression A/B where B has a static type that is an atomic type. For example, * / name().

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

SimpleMappingExpression(Expression start, Expression step, boolean isHybrid)
Constructor

Method Summary

int
computeCardinality()
Determine the static cardinality of the expression
int
computeDependencies()
Determine which aspects of the context the expression depends on.
int
computeSpecialProperties()
Get the static properties of this expression (other than its type).
Expression
copy()
Copy an expression.
boolean
equals(Object other)
Is this expression the same as another expression?
void
explain(ExpressionPresenter destination)
Diagnostic print of expression structure.
ItemType
getItemType(TypeHierarchy th)
Determine the data type of the items returned by this exprssion
Expression
getStartExpression()
Get the start expression (the left-hand operand)
Expression
getStepExpression()
Get the step expression (the right-hand operand)
boolean
hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
int
hashCode()
get HashCode for comparing two expressions
boolean
isHybrid()
Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values.
SequenceIterator
iterate(XPathContext context)
Iterate the path-expression in a given context
Iterator
iterateSubExpressions()
Get the immediate subexpressions of this expression
SequenceIterator
map(XPathContext context)
Mapping function, from a node returned by the start iteration, to a sequence returned by the child.
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expression
promote(PromotionOffer offer)
Promote this expression if possible
boolean
replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
Expression
typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

Methods inherited from class net.sf.saxon.expr.Expression

addToPathMap, adoptChildExpression, checkPermittedContents, computeCardinality, computeDependencies, computeSpecialProperties, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, explain, findParentOf, getCardinality, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getItemType, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

Constructor Details

SimpleMappingExpression

public SimpleMappingExpression(Expression start,
                               Expression step,
                               boolean isHybrid)
Constructor
Parameters:
start - A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.
step - The step to be followed from each node in the start expression to yield a new node-set
isHybrid - if true, indicates that we don't know statically whether the step expression will return nodes or atomic values. If false, we know it will return atomic values.

Method Details

computeCardinality

public int computeCardinality()
Determine the static cardinality of the expression
Overrides:
computeCardinality in interface Expression

computeDependencies

public int computeDependencies()
Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE
Overrides:
computeDependencies in interface 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.
Overrides:
computeSpecialProperties in interface Expression

copy

public Expression copy()
Copy an expression. This makes a deep copy.
Overrides:
copy in interface Expression
Returns:
the copy of the original expression

equals

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

explain

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

getItemType

public final ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this exprssion
Overrides:
getItemType in interface Expression
Parameters:
th - the type hierarchy cache
Returns:
the type of the step

getStartExpression

public Expression getStartExpression()
Get the start expression (the left-hand operand)
Returns:
the first operand

getStepExpression

public Expression getStepExpression()
Get the step expression (the right-hand operand)
Returns:
the second operand

hasLoopingSubexpression

public boolean hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
Overrides:
hasLoopingSubexpression in interface Expression
Parameters:
child - the immediate subexpression
Returns:
true if the child expression is evaluated repeatedly

hashCode

public int hashCode()
get HashCode for comparing two expressions

isHybrid

public boolean isHybrid()
Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values. If so, this needs to be prevented at run time
Returns:
true if the static type allows both nodes and atomic values

iterate

public SequenceIterator iterate(XPathContext context)
            throws XPathException
Iterate the path-expression in a given context
Specified by:
iterate in interface SequenceIterable
Overrides:
iterate in interface Expression
Parameters:
context - the evaluation context

iterateSubExpressions

public Iterator iterateSubExpressions()
Get the immediate subexpressions of this expression
Overrides:
iterateSubExpressions in interface Expression

map

public SequenceIterator map(XPathContext context)
            throws XPathException
Mapping function, from a node returned by the start iteration, to a sequence returned by the child.
Specified by:
map in interface ContextMappingFunction

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
            throws XPathException
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 interface 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
Throws:
XPathException - if an error is discovered during this phase (typically a type error)

promote

public Expression promote(PromotionOffer offer)
            throws XPathException
Promote this expression if possible
Overrides:
promote in interface Expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression
Overrides:
replaceSubExpression in interface Expression
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
Type-check the expression
Overrides:
typeCheck in interface Expression