Package net.sf.saxon.expr
Class SlashExpression
- java.lang.Object
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- net.sf.saxon.expr.Expression
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- net.sf.saxon.expr.SlashExpression
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,LocationProvider
,SaxonLocator
,ContextMappingFunction
,EvaluableItem
,SequenceIterable
,InstructionInfo
,org.xml.sax.Locator
- Direct Known Subclasses:
AtomicMappingExpression
,PathExpression
public class SlashExpression extends Expression implements 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. 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:
- Serialized Form
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Field Summary
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Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
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Constructor Summary
Constructors Constructor Description SlashExpression(Expression start, Expression step)
Constructor
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description int
computeCardinality()
Determine the static cardinality of the expressionint
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(java.lang.Object other)
Is this expression the same as another expression?void
explain(ExpressionPresenter destination)
Diagnostic print of expression structure.ItemType
getItemType(TypeHierarchy th)
Determine the data type of the items returned by this exprssionExpression
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 expressionsboolean
hasLoopingSubexpression(Expression child)
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.SequenceIterator
iterate(XPathContext context)
Iterate the path-expression in a given contextjava.util.Iterator
iterateSubExpressions()
Get 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 knownSequenceIterator
map(XPathContext context)
Mapping function, from a node returned by the start iteration, to a sequence returned by the child.Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.Expression
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)
Expression
simplify(ExpressionVisitor visitor)
Simplify an expressionExpression
typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression-
Methods 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 Detail
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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)
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Method Detail
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setStartExpression
protected void setStartExpression(Expression start2)
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setStepExpression
protected void setStepExpression(Expression step2)
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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
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getStartExpression
public Expression getStartExpression()
Get the start expression (the left-hand operand)- Returns:
- the first operand
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getStepExpression
public Expression 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
public Expression simplify(ExpressionVisitor visitor) throws XPathException
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
public final ItemType getItemType(TypeHierarchy th)
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
public Expression promote(PromotionOffer offer) throws XPathException
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
public java.util.Iterator 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
public boolean hasLoopingSubexpression(Expression child)
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
public boolean replaceSubExpression(Expression original, Expression replacement)
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
public Expression 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
public boolean equals(java.lang.Object other)
Is this expression the same as another expression?- Overrides:
equals
in classjava.lang.Object
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hashCode
public int hashCode()
get HashCode for comparing two expressions- Overrides:
hashCode
in classjava.lang.Object
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
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
public final 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 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
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 classExpression
- Parameters:
destination
- the expression presenter used to display the structure
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