Class SwitchExpression

  extended by net.sf.saxon.expr.Expression
      extended by com.saxonica.expr.SwitchExpression
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, Locator

public class SwitchExpression
extends Expression

An optimized Choose expression in which all the branches are tests of the same expression for equality with some value.

See Also:
Serialized Form

Field Summary
Fields inherited from class net.sf.saxon.expr.Expression
Constructor Summary
SwitchExpression(Expression subject, Map<Object,Expression> map, Expression defaultAction, StringCollator collation)
          Create a switch expression
Method Summary
protected  int computeCardinality()
          Compute the static cardinality of this expression
 Expression copy()
          Copy an expression.
 Item evaluateItem(XPathContext context)
          Evaluate an expression as a single item.
 void explain(ExpressionPresenter out)
          Diagnostic print of expression structure.
 ItemType getItemType(TypeHierarchy th)
          Determine the data type of the expression, if possible.
 SequenceIterator iterate(XPathContext context)
          Return an Iterator to iterate over the values of a sequence.
 Iterator<Expression> iterateSubExpressions()
          Get the immediate sub-expressions of this expression.
 void process(XPathContext context)
          Process the instruction, without returning any tail calls
 Expression promote(PromotionOffer offer, Expression parent)
          Offer promotion for this subexpression.
 boolean replaceSubExpression(Expression original, Expression replacement)
          Replace one subexpression by a replacement subexpression
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Perform type checking of an expression and its subexpressions.
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, 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, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, optimize, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeError
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail


public SwitchExpression(Expression subject,
                        Map<Object,Expression> map,
                        Expression defaultAction,
                        StringCollator collation)
Create a switch expression

subject - the value to be tested
map - a map from possible values to the action to be performed on each
defaultAction - the expression to be evaluated if the value is not found in the map
collation - the collation to be used for comparing strings
Method Detail


protected int computeCardinality()
Compute the static cardinality of this expression

Specified by:
computeCardinality in class Expression
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


public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException
Description copied from class: Expression
Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

typeCheck in class Expression
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
the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
XPathException - if an error is discovered during this phase (typically a type error)


public Expression copy()
Copy an expression. This makes a deep copy.

Specified by:
copy in class Expression
the copy of the original expression


public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:
explain in class Expression
out - the expression presenter used to display the structure


public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

This method should always return a result, though it may be the best approximation that is available at the time.

Specified by:
getItemType in class Expression
th - the type hierarchy cache
a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)


public Expression promote(PromotionOffer offer,
                          Expression parent)
                   throws XPathException
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.

promote in class Expression
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
parent -
if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
XPathException - if any error is detected


public Item evaluateItem(XPathContext context)
                  throws XPathException
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
evaluateItem in class Expression
context - The context in which the expression is to be evaluated
the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
XPathException - if any dynamic error occurs evaluating the expression


public Iterator<Expression> iterateSubExpressions()
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

iterateSubExpressions in class Expression
an iterator containing the sub-expressions of this expression


public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression

replaceSubExpression in class Expression
original - the original subexpression
replacement - the replacement subexpression
true if the original subexpression is found


public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Specified by:
iterate in interface SequenceIterable
iterate in class Expression
context - supplies the context for evaluation
a SequenceIterator that can be used to iterate over the result of the expression
XPathException - if any dynamic error occurs evaluating the expression


public void process(XPathContext context)
             throws XPathException
Process the instruction, without returning any tail calls

process in class Expression
context - The dynamic context, giving access to the current node, the current variables, etc.

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