net.sf.saxon.expr
Class SlashExpression

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.SlashExpression
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction, ContextSwitchingExpression, EvaluableItem, SequenceIterable, InstructionInfo, Locator
Direct Known Subclasses:
AtomicMappingExpression, PathExpression

public class SlashExpression
extends Expression
implements ContextMappingFunction, ContextSwitchingExpression

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

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
 
Constructor Summary
SlashExpression(Expression start, Expression step)
          Constructor
 
Method Summary
 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)
 Expression getFirstStep()
          Get the first step in this expression.
 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.
 int hashCode()
          get HashCode for comparing two expressions
 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
 boolean 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 context
 Iterator<Expression> 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.
 Iterator<Expression> iterateSubExpressions()
          Get the immediate subexpressions of this expression
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
 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, ItemType 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, 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 expression
 boolean replaceSubExpression(Expression original, Expression replacement)
          Replace one subexpression by a replacement subexpression
protected  void setStartExpression(Expression start2)
           
protected  void setStepExpression(Expression step2)
           
 Expression simplify(ExpressionVisitor visitor)
          Simplify an expression
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Type-check the expression
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, 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

protected void setStartExpression(Expression start2)

setStepExpression

protected void setStepExpression(Expression step2)

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


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

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

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

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType 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,
                           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 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)

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 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

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
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

iterateSameFocusSubExpressions

public Iterator<Expression> 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 class Expression
Returns:
an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression

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 class Expression
Parameters:
child - the immediate subexpression
Returns:
true if the child expression is evaluated repeatedly

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

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

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 iterate(XPathContext context)
                         throws XPathException
Iterate the path-expression in a given context

Specified by:
iterate in interface SequenceIterable
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 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 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

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

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


Copyright (c) Saxonica Limited. All rights reserved.