net.sf.saxon.expr

Class SimpleMappingExpression

java.lang.Object

net.sf.saxon.expr.ComputedExpression

net.sf.saxon.expr.SimpleMappingExpression

All Implemented Interfaces:

java.io.Serializable, javax.xml.transform.SourceLocator, Container, ContextMappingFunction, Expression, InstructionInfoProvider

public final class SimpleMappingExpression
extends ComputedExpression
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().

See Also:

Serialized Form

Field Summary

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

locationId, staticProperties

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method and Description
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).
void	display(int level, java.io.PrintStream out, Configuration config) Diagnostic print of expression structure
boolean	equals(java.lang.Object other) Is this expression the same as another expression?
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)
int	hashCode() get HashCode for comparing two expressions
SequenceIterator	iterate(XPathContext context) Iterate the path-expression in a given context
java.util.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(Optimizer opt, StaticContext env, 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(StaticContext env, ItemType contextItemType) Type-check the expression

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

adoptChildExpression, checkPermittedContents, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, simplify, suppressValidation, typeError

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

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 Detail

getStartExpression

public Expression getStartExpression()

Get the start expression (the left-hand operand)

getStepExpression

public Expression getStepExpression()

Get the step expression (the right-hand operand)

getItemType

public final ItemType getItemType(TypeHierarchy th)

Determine the data type of the items returned by this exprssion

Specified by:

getItemType in interface Expression

Parameters:

th -

Returns:

the type of the step

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)

Type-check the expression

Specified by:

typeCheck in interface Expression

Parameters:

env - the static context of the expression

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(Optimizer opt,
                           StaticContext env,
                           ItemType contextItemType)

Description copied from interface: 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.

Specified by:

optimize in interface Expression

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

env - the static context of the expression

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

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Promote this expression if possible

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

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()

Get the immediate subexpressions of this expression

Specified by:

iterateSubExpressions in interface Expression

Overrides:

iterateSubExpressions in class ComputedExpression

Returns:

an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Specified by:

replaceSubExpression in interface Container

Overrides:

replaceSubExpression in class ComputedExpression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

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 class ComputedExpression

Returns:

the depencies, as a bit-mask

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 class ComputedExpression

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Specified by:

computeCardinality in class ComputedExpression

equals

public boolean equals(java.lang.Object other)

Is this expression the same as another expression?

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

get HashCode for comparing two expressions

Overrides:

hashCode in class java.lang.Object

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate the path-expression in a given context

Specified by:

iterate in interface Expression

Overrides:

iterate in class ComputedExpression

Parameters:

context - the evaluation context

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

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

Parameters:

context - The processing context. The item to be mapped is the context item identified from this context: the values of position() and last() also relate to the set of items being mapped

Returns:

a SequenceIterator over the sequence of items that the supplied input item maps to

Throws:

XPathException

display

public void display(int level,
                    java.io.PrintStream out,
                    Configuration config)

Diagnostic print of expression structure

Specified by:

display in interface Expression

Parameters:

level - indentation level for this expression

out - Output destination