java.lang.Object
- net.sf.saxon.expr.Expression
- - net.sf.saxon.expr.SlashExpression

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

Field Summary
- Fields inherited from class net.sf.saxon.expr.Expression
  EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties

Constructor Summary

Constructors
Constructor Description

SlashExpression(Expression start, Expression step)
Constructor

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`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(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 exprssion
`Expression`	`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 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
`java.util.Iterator`	`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)`	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, 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

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
  - getStartExpression
```
public Expression getStartExpression()
```
    Get the start expression (the left-hand operand)
    
    Returns:
    
    the first operand
  - getStepExpression
```
public Expression getStepExpression()
```
    Get the step expression (the right-hand operand)
    
    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)
                   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 java.util.Iterator iterateSubExpressions()
```
    Get the immediate subexpressions of this expression
    
    Overrides:
    
    iterateSubExpressions in class Expression
    
    Returns:
    
    an iterator containing the sub-expressions of this 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(java.lang.Object other)
```
    Is this expression the same as another expression?
    
    Overrides:
    
    equals in class java.lang.Object
  - hashCode
```
public int hashCode()
```
    get HashCode for comparing two expressions
    
    Overrides:
    
    hashCode in class java.lang.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

Class SlashExpression

Field Summary

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

Constructor Summary

Method Summary

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

Methods inherited from class java.lang.Object

Constructor Detail

SlashExpression

Method Detail

setStartExpression

setStepExpression

makeSlashExpression

getStartExpression

getStepExpression

isHybrid

simplify

getItemType

typeCheck

optimize

promoteFocusIndependentSubexpressions

promote

iterateSubExpressions

hasLoopingSubexpression

replaceSubExpression

computeDependencies

copy

computeSpecialProperties

computeCardinality

equals

hashCode

iterate

map

explain