Package 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:
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Field Summary
FieldsFields inherited from class net.sf.saxon.expr.Expression
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionaddToPathMap
(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.int
Determine the static cardinality of the expressionint
Determine which aspects of the context the expression depends on.int
Get the static properties of this expression (other than its type).copy()
Copy an expression.boolean
Is this expression the same as another expression?void
explain
(ExpressionPresenter destination) Diagnostic print of expression structure.Get the step expression (the right-hand operand)Get the start expression (the left-hand operand)Get the first step in this expression.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.final ItemType
Determine the data type of the items returned by this exprssionGet the last step of the path expressionGet a path expression consisting of all steps except the lastGet all steps after the first.getStep()
Get step of the path expressionint
hashCode()
get HashCode for comparing two expressionsboolean
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 repeatedlyboolean
Test whether a path expression is an absolute path - that is, a path whose first step selects a document nodeSequenceIterator<? extends Item>
iterate
(XPathContext context) Iterate the path-expression in a given contextGet the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.Get the immediate subexpressions of this expressionmap
(XPathContext context) Mapping function, from a node returned by the start iteration, to a sequence returned by the child.optimize
(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform optimisation of an expression and its subexpressions.promote
(PromotionOffer offer, Expression parent) Promote this expression if possibleprotected 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 expressionboolean
replaceSubExpression
(Expression original, Expression replacement) Replace one subexpression by a replacement subexpressionvoid
setStartExpression
(Expression start2) void
setStepExpression
(Expression step2) simplify
(ExpressionVisitor visitor) Simplify an expressiontoString()
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.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.typeCheck
(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Type-check the expressionMethods 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
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Field Details
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start
Expression start -
step
Expression step
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Constructor Details
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SlashExpression
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)
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Method Details
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setStartExpression
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setStepExpression
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getControllingExpression
Get the start expression (the left-hand operand)- Specified by:
getControllingExpression
in interfaceContextSwitchingExpression
- Returns:
- the first operand
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getControlledExpression
Get the step expression (the right-hand operand)- Specified by:
getControlledExpression
in interfaceContextSwitchingExpression
- Returns:
- the second operand
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simplify
Simplify an expression- Overrides:
simplify
in classExpression
- Parameters:
visitor
- the expression visitor- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
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getItemType
Determine the data type of the items returned by this exprssion- Specified by:
getItemType
in classExpression
- Parameters:
th
- the type hierarchy cache- Returns:
- the type of the step
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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 classExpression
- Returns:
- the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.
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typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException Type-check the expression- Overrides:
typeCheck
in classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
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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 classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
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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- 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.
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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 visitorcontextItemType
- 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
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promote
Promote this expression if possible- Overrides:
promote
in classExpression
- 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 expressionparent
- 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
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iterateSubExpressions
Get the immediate subexpressions of this expression- Overrides:
iterateSubExpressions
in classExpression
- Returns:
- an iterator containing the sub-expressions of this expression
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iterateSameFocusSubExpressions
Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.- Overrides:
iterateSameFocusSubExpressions
in classExpression
- Returns:
- an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression
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hasLoopingSubexpression
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 classExpression
- Parameters:
child
- the immediate subexpression- Returns:
- true if the child expression is evaluated repeatedly
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replaceSubExpression
Replace one subexpression by a replacement subexpression- Overrides:
replaceSubExpression
in classExpression
- Parameters:
original
- the original subexpressionreplacement
- the replacement subexpression- Returns:
- true if the original subexpression is found
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addToPathMap
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 classExpression
- Parameters:
pathMap
- the PathMap to which the expression should be addedpathMapNodeSet
-- 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
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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 classExpression
- Returns:
- the depencies, as a bit-mask
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copy
Copy an expression. This makes a deep copy.- Specified by:
copy
in classExpression
- Returns:
- the copy of the original expression
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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 classExpression
- Returns:
- the special properties, as a bit-significant integer
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computeCardinality
public int computeCardinality()Determine the static cardinality of the expression- Specified by:
computeCardinality
in classExpression
- 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
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equals
Is this expression the same as another expression? -
hashCode
public int hashCode()get HashCode for comparing two expressions -
iterate
Iterate the path-expression in a given context- Overrides:
iterate
in classExpression
- 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
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map
Mapping function, from a node returned by the start iteration, to a sequence returned by the child.- Specified by:
map
in interfaceContextMappingFunction<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
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explain
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
explain
in classExpression
- Parameters:
destination
- the expression presenter used to display the structure
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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 classExpression
- Returns:
- a representation of the expression as a string
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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
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getStep
Get step of the path expression- Returns:
- the step expression
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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
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getLastStep
Get the last step of the path expression- Returns:
- the last step in the expression, after expanding any nested path expressions
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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
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isAbsolute
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
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