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
,EvaluableItem
,SequenceIterable
,InstructionInfo
,Locator
- Direct Known Subclasses:
AtomicMappingExpression
,PathExpression
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
AtomicMappingExpressions (returning 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
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionint
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.final ItemType
Determine the data type of the items returned by this exprssionGet the start expression (the left-hand operand)Get the step expression (the right-hand operand)int
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
isHybrid()
Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values.iterate
(XPathContext context) Iterate the path-expression in a given contextGet the immediate subexpressions of this expressionstatic SlashExpression
makeSlashExpression
(Expression start, Expression step, TypeHierarchy th) Static factory method, allowing early instantiation of a subclass if the type of the step expression is already knownfinal SequenceIterator
map
(XPathContext context) Mapping function, from a node returned by the start iteration, to a sequence returned by the child.optimize
(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.promote
(PromotionOffer offer) Promote this expression if possibleprotected Expression
promoteFocusIndependentSubexpressions
(ExpressionVisitor visitor, ItemType 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 subexpressionprotected void
setStartExpression
(Expression start2) protected void
setStepExpression
(Expression step2) simplify
(ExpressionVisitor visitor) Simplify an expressiontypeCheck
(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expressionMethods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeStaticProperties, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, typeError
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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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makeSlashExpression
public static SlashExpression makeSlashExpression(Expression start, Expression step, TypeHierarchy th) Static factory method, allowing early instantiation of a subclass if the type of the step expression is already known -
getStartExpression
Get the start expression (the left-hand operand)- Returns:
- the first operand
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getStepExpression
Get the step expression (the right-hand operand)- Returns:
- the second operand
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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
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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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typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ItemType 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, ItemType 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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promoteFocusIndependentSubexpressions
protected Expression promoteFocusIndependentSubexpressions(ExpressionVisitor visitor, ItemType 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
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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 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
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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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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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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- Specified by:
iterate
in interfaceSequenceIterable
- 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
- 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
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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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