## com.saxonica.expr
Class IndexedLookupExpression

    java.lang.Object
      net.sf.saxon.expr.Expression
          com.saxonica.expr.IndexedLookupExpression

All Implemented Interfaces:
  Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, Locator

    public final class IndexedLookupExpression

extends Expression

An IndexedLookupExpression contains a base expression and a lookup expression. The base expression will always be a local variable reference. The expression returns true if the base expression (after atomization) contains the value of the lookup expression. That is, the expression is equivalent to exists(base[lookup]), except that lookup is evaluated with the same context as base.

See Also:
  Serialized Form

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression
`EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, PUSH_SELECTION, staticProperties, WATCH_METHOD`

Constructor Summary
`IndexedLookupExpression(VariableReference base, Expression lookup, AtomicComparer comparer)` Constructor

Method Summary
`int` `computeCardinality()` Get the static cardinality of this 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` `effectiveBooleanValue(XPathContext context)` Get the effective boolean value of the expression.
`boolean` `equals(Object other)` Is this expression the same as another expression?
`Item` `evaluateItem(XPathContext context)` Evaluate an expression as a single item.
`void` `explain(ExpressionPresenter destination)` Diagnostic print of expression structure.
`AtomicComparer` `getAtomicComparer()` Get the atomic comparer used
`Expression` `getBaseExpression()` Get the underlying expression
`ItemType` `getItemType(TypeHierarchy th)` Get the data type of the items returned
`Expression` `getLookup()` Get the lookup expression
`Expression` `getLookupExpression()` Get the expression to be searched
`int` `hashCode()` get HashCode for comparing two expressions
`Iterator<Expression>` `iterateSubExpressions()` Get the immediate subexpressions of this expression
`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
`boolean` `replaceSubExpression(Expression original, Expression replacement)` Replace one subexpression by a replacement subexpression
`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, evaluateAsString, 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, hasLoopingSubexpression, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, typeError`

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

Constructor Detail

### IndexedLookupExpression

    public IndexedLookupExpression(VariableReference base,
                                   Expression lookup,
                                   AtomicComparer comparer)

  Constructor

  Parameters:
    `base` - A sequence expression denoting the sequence to be searched
    `lookup` - An expression defining value to be sought

Method Detail

### getItemType

    public ItemType getItemType(TypeHierarchy th)

  Get the data type of the items returned

  Specified by:
    `getItemType` in class `Expression`
  Parameters:
    `th` - the type hierarchy cache
  Returns:
    an integer representing the data type

### getBaseExpression

    public Expression getBaseExpression()

  Get the underlying expression

  Returns:
    the expression being filtered

### getLookup

    public Expression getLookup()

  Get the lookup expression

  Returns:
    the expression acting as the filter predicate

### getLookupExpression

    public Expression getLookupExpression()

  Get the expression to be searched

  Returns:
    the expression whose value will be searched

### getAtomicComparer

    public AtomicComparer getAtomicComparer()

  Get the atomic comparer used

  Returns:
    the atomic comparer

### simplify

    public Expression simplify(ExpressionVisitor visitor)
                        throws XPathException

  Simplify an expression

  Overrides:
    `simplify` in class `Expression`
  Parameters:
    `visitor` - an expression visitor
  Returns:
    the simplified expression
  Throws:
    `XPathException` - if an error is discovered during expression rewriting

### typeCheck

    public Expression typeCheck(ExpressionVisitor visitor,
                                ItemType contextItemType)

  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 expression after type-checking (potentially modified to add run-time checks and/or conversions)

### optimize

    public Expression optimize(ExpressionVisitor visitor,
                               ItemType contextItemType)

  Perform optimisation of an expression and its subexpressions.

  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

### 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

### 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 promotion that is possible
    `parent` -
  Returns:
    the promoted expression (or the original expression, unchanged)
  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:
    the subexpressions, as an array

### 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

### computeCardinality

    public int computeCardinality()

  Get the static cardinality of this expression

  Specified by:
    `computeCardinality` in class `Expression`
  Returns:
    the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered

### computeSpecialProperties

    public int computeSpecialProperties()

  Get the static properties of this expression (other than its type). The result is bit-significant. 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 static properties of the expression, as a bit-significant value

### equals

    public boolean equals(Object other)

  Is this expression the same as another expression?

  Overrides:
    `equals` in class `Object`
  Parameters:
    `other` - the expression to be compared with this one
  Returns:
    true if the two expressions are statically equivalent

### hashCode

    public int hashCode()

  get HashCode for comparing two expressions

  Overrides:
    `hashCode` in class `Object`
  Returns:
    the hash code

### effectiveBooleanValue

    public boolean effectiveBooleanValue(XPathContext context)
                                  throws XPathException

  Description copied from class: `Expression`
  Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

  Overrides:
    `effectiveBooleanValue` in class `Expression`
  Parameters:
    `context` - The context in which the expression is to be evaluated
  Returns:
    the effective boolean value
  Throws:
    `XPathException` - if any dynamic error occurs evaluating the expression

### evaluateItem

    public Item evaluateItem(XPathContext context)
                      throws XPathException

  Description copied from class: `Expression`
  Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

  Specified by:
    `evaluateItem` in interface `EvaluableItem`
  Overrides:
    `evaluateItem` in class `Expression`
  Parameters:
    `context` - The context in which the expression is to be evaluated
  Returns:
    the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
  Throws:
    `XPathException` - if any dynamic error occurs evaluating the expression

### 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 dependencies

### 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

Copyright (c) 2004-2010 Saxonica Limited. All rights reserved.