net.sf.saxon.expr

Class SlashExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.BinaryExpression

net.sf.saxon.expr.SlashExpression

All Implemented Interfaces:

ContextMappingFunction, ContextOriginator, ContextSwitchingExpression, IdentityComparable

Direct Known Subclasses:

SimpleStepExpression

public class SlashExpression
extends BinaryExpression
implements ContextSwitchingExpression, ContextMappingFunction

A slash expression is any expression using the binary slash operator "/". The parser initially generates a slash expression for all occurrences of the binary "/" operator, wrapped in a documentSort() function to do the sorting and de-duplication required by the semantics of path expressions. The documentSort() is subsequently stripped off by the optimizer if sorting and deduplication is found to be unnecessary. The slash expression itself, therefore, does not perform sorting or de-duplication.

Field Summary

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

operator

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
SlashExpression(Expression start, Expression step) Constructor

Method Summary

Methods

Modifier and Type	Method and Description
PathMap.PathMapNodeSet	addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.
int	computeCardinality() Determine the static cardinality of the expression
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
SlashExpression	copy() Copy an expression.
boolean	equals(Object other) Is this expression the same as another expression?
void	export(ExpressionPresenter destination) Diagnostic print of expression structure.
Expression	getActionExpression() Get the step expression (the right-hand operand)
int	getCost() Return the estimated cost of evaluating an expression.
ExpressionCompiler	getExpressionCompiler() Return the compiler of the Slash expression
String	getExpressionName() Get a name identifying the kind of expression, in terms meaningful to a user.
Expression	getFirstStep() Get the first step in this expression.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
IntegerValue[]	getIntegerBounds() For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis.
ItemType	getItemType() Determine the data type of the items returned by this exprssion
Expression	getLastStep() Get the last step of the path expression
Expression	getLeadingSteps() Get a path expression consisting of all steps except the last
protected OperandRole	getOperandRole(int arg) Get the operand role
Expression	getRemainingSteps() Get all steps after the first.
Expression	getSelectExpression() Get the start expression (the left-hand operand)
Expression	getStart() Get the left-hand operand
Expression	getStep() Get the right-hand operand
ForEachAdjunct	getStreamingAdjunct() Get a class that supports streamed evaluation of this expression
int	hashCode() get HashCode for comparing two expressions
boolean	isAbsolute() Test whether a path expression is an absolute path - that is, a path whose first step selects a document node
SequenceIterator	iterate(XPathContext context) Iterate the path-expression in a given context
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, ContextItemStaticInfo contextItemType) Perform optimisation of an expression and its subexpressions.
void	promoteChildren(PromotionOffer offer) Promote this expression if possible
protected Expression	promoteFocusIndependentSubexpressions(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) If any subexpressions within the step are not dependent on the focus, and if they are not "creative" expressions (expressions that can create new nodes), then promote them: this causes them to be evaluated once, outside the path expression
void	setStart(Expression start) Set the left-hand operand
void	setStep(Expression step) Set the right-hand operand
Pattern	toPattern(Configuration config, boolean is30) Convert this expression to an equivalent XSLT pattern
String	toShortString() Produce a short string identifying the expression for use in error messages
String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
SlashExpression	tryToMakeAbsolute() Test whether a path expression is an absolute path - that is, a path whose first step selects a document node; if not, see if it can be converted to an absolute path.
Expression	tryToMakeSorted(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType)
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Type-check the expression
Expression	unordered(boolean retainAllNodes, boolean forStreaming) Replace this expression by a simpler expression that delivers the results without regard to order.

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

displayOperator, explainExtraAttributes, getLhs, getLhsExpression, getOperator, getRhs, getRhsExpression, isAssociative, isCommutative, isInverse, operands, setFlattened, setLhsExpression, setRhsExpression, tag

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

adoptChildExpression, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, clearStreamabilityData, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getDependencies, getEvaluationMethod, getHostLanguage, getIntrinsicDependencies, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getPosture, getPostureAndSweepIfKnown, getProperties, getProperty, getRetainedStaticContext, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStreamability, getSweep, getSystemId, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isCallOnSystemFunction, isIdentical, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, makeStreamingAdjunct, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, optimizeForType, process, promote, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setFiltered, setLocation, setParentExpression, setPostureAndSweep, setRetainedStaticContext, setRetainedStaticContextLocally, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toStreamingPattern, typeCheckChildren, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

SlashExpression

public SlashExpression(Expression start,
               Expression step)

Constructor

Parameters:

start - The left hand operand (which must always select a sequence of nodes).

step - The step to be followed from each node in the start expression to yield a new sequence; this may return either nodes or atomic values (but not a mixture of the two)

Method Detail

getOperandRole

protected OperandRole getOperandRole(int arg)

Description copied from class: BinaryExpression

Get the operand role

Overrides:

getOperandRole in class BinaryExpression

Parameters:

arg - which argument: 0 for the lhs, 1 for the rhs

Returns:

the operand role

getStart

public Expression getStart()

Get the left-hand operand

Returns:

the left-hand operand

setStart

public void setStart(Expression start)

Set the left-hand operand

Parameters:

start - the left-hand operand

getStep

public Expression getStep()

Get the right-hand operand

Returns:

the right-hand operand

setStep

public void setStep(Expression step)

Set the right-hand operand

Parameters:

step - the right-hand operand

getExpressionName

public String getExpressionName()

Description copied from class: Expression

Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:

getExpressionName in class Expression

Returns:

a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in export() output displaying the expression.

getSelectExpression

public Expression getSelectExpression()

Get the start expression (the left-hand operand)

Specified by:

getSelectExpression in interface ContextSwitchingExpression

Returns:

the first operand

getActionExpression

public Expression getActionExpression()

Get the step expression (the right-hand operand)

Specified by:

getActionExpression in interface ContextSwitchingExpression

Returns:

the second operand

getItemType

public final ItemType getItemType()

Determine the data type of the items returned by this exprssion

Specified by:

getItemType in class Expression

Returns:

the type of the step

getIntegerBounds

public IntegerValue[] getIntegerBounds()

For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.

Overrides:

getIntegerBounds in class Expression

Returns:

the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                   ContextItemStaticInfo contextInfo)
                     throws XPathException

Type-check the expression

Overrides:

typeCheck in class BinaryExpression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

Returns:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                  ContextItemStaticInfo contextItemType)
                    throws XPathException

Description copied from class: BinaryExpression

Perform optimisation of an expression and its subexpressions.

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 BinaryExpression

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)

tryToMakeAbsolute

public SlashExpression tryToMakeAbsolute()

Test whether a path expression is an absolute path - that is, a path whose first step selects a document node; if not, see if it can be converted to an absolute path. This is possible in cases where the path expression has the form a/b/c and it is known that the context item is a document node; in this case it is safe to change the path expression to /a/b/c

Returns:

the path expression if it is absolute; the converted path expression if it can be made absolute; or null if neither condition applies.

getCost

public int getCost()

Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.

Overrides:

getCost in class Expression

Returns:

an estimate of the gross cost of evaluating the expression, including the cost of evaluating its operands.

tryToMakeSorted

public Expression tryToMakeSorted(ExpressionVisitor visitor,
                         ContextItemStaticInfo contextItemType)
                           throws XPathException

Throws:

XPathException

promoteFocusIndependentSubexpressions

protected Expression promoteFocusIndependentSubexpressions(ExpressionVisitor visitor,
                                               ContextItemStaticInfo contextItemType)
                                                    throws XPathException

If any subexpressions within the step are not dependent on the focus, and if they are not "creative" expressions (expressions that can create new nodes), then promote them: this causes them to be evaluated once, outside the path expression

Parameters:

visitor - the expression visitor

contextItemType - the type of the context item for evaluating the start expression

Returns:

the rewritten expression, or the original expression if no rewrite was possible

Throws:

XPathException - if a static error is detected

promoteChildren

public void promoteChildren(PromotionOffer offer)
                     throws XPathException

Promote this expression if possible

Overrides:

promoteChildren in class Expression

Parameters:

offer - the promotion offer

Throws:

XPathException - if any failure occurs

unordered

public Expression unordered(boolean retainAllNodes,
                   boolean forStreaming)
                     throws XPathException

Replace this expression by a simpler expression that delivers the results without regard to order.

Overrides:

unordered in class Expression

Parameters:

retainAllNodes - set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.

forStreaming - set to true if optimizing for streaming

Returns:

an expression that delivers the same nodes in a more convenient order

Throws:

XPathException - if the rewrite fails

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                  PathMap.PathMapNodeSet pathMapNodeSet)

Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

Overrides:

addToPathMap in class Expression

Parameters:

pathMap - the PathMap to which the expression should be added

pathMapNodeSet -

Returns:

the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression

getImplementationMethod

public int getImplementationMethod()

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.

Overrides:

getImplementationMethod in class BinaryExpression

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

copy

public SlashExpression copy()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original 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 class BinaryExpression

Returns:

StaticProperty.NON_CREATIVE. This is overridden for some subclasses.

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Overrides:

computeCardinality in class BinaryExpression

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

toPattern

public Pattern toPattern(Configuration config,
                boolean is30)
                  throws XPathException

Convert this expression to an equivalent XSLT pattern

Overrides:

toPattern in class Expression

Parameters:

config - the Saxon configuration

is30 - true if this is XSLT 3.0

Returns:

the equivalent pattern

Throws:

XPathException - if conversion is not possible

equals

public boolean equals(Object other)

Is this expression the same as another expression?

Overrides:

equals in class BinaryExpression

hashCode

public int hashCode()

get HashCode for comparing two expressions

Overrides:

hashCode in class BinaryExpression

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate the path-expression in a given context

Overrides:

iterate in class Expression

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 - if a dynamic error is detected

export

public void export(ExpressionPresenter destination)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Overrides:

export in class BinaryExpression

Parameters:

destination - the output destination for the displayed expression tree

toString

public String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

Overrides:

toString in class BinaryExpression

Returns:

a representation of the expression as a string

toShortString

public String toShortString()

Description copied from class: Expression

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class BinaryExpression

Returns:

a short string, sufficient to identify the expression

getFirstStep

public Expression getFirstStep()

Get the first step in this expression. A path expression A/B/C is represented as (A/B)/C, but the first step is A

Returns:

the first step in the expression, after expanding any nested path expressions

getRemainingSteps

public Expression getRemainingSteps()

Get all steps after the first. This is complicated by the fact that A/B/C is represented as ((A/B)/C; we are required to return B/C

Returns:

a path expression containing all steps in this path expression other than the first, after expanding any nested path expressions

getLastStep

public Expression getLastStep()

Get the last step of the path expression

Returns:

the last step in the expression, after expanding any nested path expressions

getLeadingSteps

public Expression getLeadingSteps()

Get a path expression consisting of all steps except the last

Returns:

a path expression containing all steps in this path expression other than the last, after expanding any nested path expressions

isAbsolute

public boolean isAbsolute()

Test whether a path expression is an absolute path - that is, a path whose first step selects a document node

Returns:

true if the first step in this path expression selects a document node

getStreamingAdjunct

public ForEachAdjunct getStreamingAdjunct()

Get a class that supports streamed evaluation of this expression

Overrides:

getStreamingAdjunct in class Expression

Returns:

the relevant StreamingAdjunct, or null if none is available

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the Slash expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler