net.sf.saxon.expr

Class SlashExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.SlashExpression

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction<Item>, ContextSwitchingExpression, InstructionInfo, Locator

Direct Known Subclasses:

SimpleStepExpression

public class SlashExpression
extends Expression
implements ContextSwitchingExpression, ContextMappingFunction<Item>

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. Subsequently, as a result of type inferencing, the majority of slash expressions will be rewritten as instances of PathExpression (returning nodes) or ForEach instructions (when they return atomic values). However, in the rare case where it is not possible to determine statically whether the rh operand returns nodes or atomic values, instances of this class may need to be interpreted directly at run time.

See Also:

Serialized Form

Field Summary

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, INHERITED_CONTEXT, INSPECTION_CONTEXT, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, NAVIGATION_CONTEXT, NODE_VALUE_CONTEXT, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, W3C_CONSUMING, W3C_FREE_RANGING, W3C_GROUP_CONSUMING, W3C_MOTIONLESS, 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	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.
Expression	getControlledExpression() Get the step expression (the right-hand operand)
Expression	getControllingExpression() Get the start expression (the left-hand operand)
ExpressionCompiler	getExpressionCompiler() Return the compiler of the Slash expression
Expression	getFirstStep() Get the first step in this expression.
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(TypeHierarchy th) 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
Expression	getRemainingSteps() Get all steps after the first.
Expression	getStep() Get step of the path expression
int	getStreamability(int syntacticContext, boolean allowExtensions, List<String> reasons) Get the "sweep" of this expression as defined in the W3C streamability specifications.
ForEachAdjunct	getStreamingAdjunct() Get a class that supports streamed evaluation of this expression
int	hashCode() get HashCode for comparing two expressions
boolean	isAbsolute(TypeHierarchy th) Test whether a path expression is an absolute path - that is, a path whose first step selects a document node
static boolean	isInheritedAttributePath(Expression exp) Tests whether a path selects attributes of ancestor elements: this has special significance for streamability analysis.
static boolean	isPermittedAxis(byte axis)
SequenceIterator<? extends Item>	iterate(XPathContext context) Iterate the path-expression in a given context
Iterator<SubExpressionInfo>	iterateSubExpressionInfo() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
Iterator<Expression>	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, ExpressionVisitor.ContextItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer, Expression parent) Promote this expression if possible
protected Expression	promoteFocusIndependentSubexpressions(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType 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
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
void	setStartExpression(Expression start2)
void	setStepExpression(Expression step2)
Expression	simplify(ExpressionVisitor visitor) Simplify an expression
Pattern	toPattern(Configuration config, boolean is30) Convert this expression to an equivalent XSLT pattern
Pattern	toStreamingPattern(Configuration config, List<String> reasonForFailure) Convert this expression to a streaming pattern (a pattern used internally to match nodes during push processing of an event stream)
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(TypeHierarchy th) 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	typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Type-check the expression

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

adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getExpressionName, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, 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

setStartExpression

public void setStartExpression(Expression start2)

setStepExpression

public void setStepExpression(Expression step2)

getControllingExpression

public Expression getControllingExpression()

Get the start expression (the left-hand operand)

Specified by:

getControllingExpression in interface ContextSwitchingExpression

Returns:

the first operand

getControlledExpression

public Expression getControlledExpression()

Get the step expression (the right-hand operand)

Specified by:

getControlledExpression in interface ContextSwitchingExpression

Returns:

the second operand

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Simplify an expression

Overrides:

simplify in class Expression

Parameters:

visitor - the expression visitor

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

getItemType

public final ItemType getItemType(TypeHierarchy th)

Determine the data type of the items returned by this exprssion

Specified by:

getItemType in class Expression

Parameters:

th - the type hierarchy cache

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,
                   ExpressionVisitor.ContextItemType contextItemType)
                     throws XPathException

Type-check the expression

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

Throws:

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

optimize

public Expression optimize(ExpressionVisitor visitor,
                  ExpressionVisitor.ContextItemType contextItemType)
                    throws XPathException

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

Throws:

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

tryToMakeAbsolute

public SlashExpression tryToMakeAbsolute(TypeHierarchy th)

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

Parameters:

th - the type hierarchy cache

Returns:

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

promoteFocusIndependentSubexpressions

protected Expression promoteFocusIndependentSubexpressions(ExpressionVisitor visitor,
                                               ExpressionVisitor.ContextItemType 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

promote

public Expression promote(PromotionOffer offer,
                 Expression parent)
                   throws XPathException

Promote this expression if possible

Overrides:

promote in class Expression

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

parent - the containing expression in the expression tree

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 Iterator<Expression> iterateSubExpressions()

Get the immediate subexpressions of this expression

Overrides:

iterateSubExpressions in class Expression

Returns:

an iterator containing the sub-expressions of this expression

iterateSubExpressionInfo

public Iterator<SubExpressionInfo> iterateSubExpressionInfo()

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Overrides:

iterateSubExpressionInfo in class Expression

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

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

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

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 Expression

Returns:

the depencies, as a bit-mask

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

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 Expression

Returns:

the special properties, as a bit-significant integer

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Specified by:

computeCardinality in class Expression

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 Object

hashCode

public int hashCode()

get HashCode for comparing two expressions

Overrides:

hashCode in class Object

iterate

public SequenceIterator<? extends Item> 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<Item>

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

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

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 Expression

Returns:

a representation of the expression as a string

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

getStep

public Expression getStep()

Get step of the path expression

Returns:

the step expression

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(TypeHierarchy th)

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

Parameters:

th - the type hierarchy cache

Returns:

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

isInheritedAttributePath

public static boolean isInheritedAttributePath(Expression exp)

Tests whether a path selects attributes of ancestor elements: this has special significance for streamability analysis. More specifically, if a path consists entirely of steps using the parent, ancestor, self, ancestor-or-self, attribute and namespace axes, optionally filtered by motionless predicates, then the expression is motionless provided that it is used in a boolean, atomizing, or inspection context (to ensure that the selected nodes cannot be used as the basis for further navigation)

Parameters:

exp - the expression being tested

Returns:

true if this is a path using the permitted axes together with motionless predicates

isPermittedAxis

public static boolean isPermittedAxis(byte axis)

getStreamability

public int getStreamability(int syntacticContext,
                   boolean allowExtensions,
                   List<String> reasons)

Get the "sweep" of this expression as defined in the W3C streamability specifications. This provides an assessment of stylesheet code against the W3C criteria for guaranteed streamability, and is implemented to allow these criteria to be tested. It is not the case that all expression that emerge as streamable from this analysis are currently capable of being streamed by Saxon

Overrides:

getStreamability in class Expression

Parameters:

syntacticContext - one of the values Expression.NAVIGATION_CONTEXT, Expression.NODE_VALUE_CONTEXT, Expression.INHERITED_CONTEXT, Expression.INSPECTION_CONTEXT

allowExtensions - if false, the definition of "guaranteed streamability" in the W3C specification is used. If true, Saxon extensions are permitted, which make some constructs streamable that would not be so according to W3C rules.

reasons -

Returns:

one of the values Expression.W3C_MOTIONLESS, Expression.W3C_CONSUMING, Expression.W3C_GROUP_CONSUMING, Expression.W3C_FREE_RANGING

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

toStreamingPattern

public Pattern toStreamingPattern(Configuration config,
                         List<String> reasonForFailure)

Convert this expression to a streaming pattern (a pattern used internally to match nodes during push processing of an event stream)

Overrides:

toStreamingPattern in class Expression

Parameters:

config - the Saxon configuration

reasonForFailure - a list which will be populated with messages giving reasons why the expression cannot be converted

Returns:

the equivalent pattern if conversion succeeds; otherwise null

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the Slash expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler