Class ComputedExpression
- All Implemented Interfaces:
Serializable
,SourceLocator
,Container
,Expression
,InstructionInfoProvider
- Direct Known Subclasses:
Assignation
,AxisExpression
,BinaryExpression
,CompareToIntegerConstant
,ContextItemExpression
,ErrorExpression
,FilterExpression
,FunctionCall
,IfExpression
,Instruction
,IntegerRangeTest
,IsLastExpression
,NumberInstruction
,PathExpression
,PositionRange
,SimpleContentConstructor
,SimpleExpression
,SimpleMappingExpression
,SingleNodeExpression
,SliceExpression
,SortExpression
,SuppliedParameterReference
,TailExpression
,TupleExpression
,TupleSorter
,UnaryExpression
,VariableReference
This class is an abstract superclass for different kinds of expression. This includes XSLT instructions, which are treated just like XPath expressions. Every expression is either a constant Value, or a ComputedExpression.
There are three principal methods for evaluating an expression: iterate(), which an iterator over the result of the expression as a sequence; evaluateItem(), which returns an object that is an instance of net.sf.saxon.om.Item; and process(), which pushes the results of the expression to a Receiver. All three methods take an XPathContext object to supply the evaluation context; for an expression that is a Value, this argument is ignored and may be null. This root class provides an implementation of iterate() in terms of evaluateItem() that works only for singleton expressions, and an implementation of evaluateItem() in terms of iterate() that works only for non-singleton expressions. Subclasses of expression must therefore provide either iterate() or evaluateItem() or process(): they do not have to provide all three.
Note that the methods that take an XPathContext argument are run-time methods. The methods without such an argument are compile-time methods. Run-time methods must not modify the state of the Expression object.
- See Also:
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Field Summary
FieldsFields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
adoptChildExpression
(Expression child) Set up a parent-child relationship between this expression and a given child expression.void
checkPermittedContents
(SchemaType parentType, StaticContext env, boolean whole) Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.protected abstract int
int
Compute the dependencies of an expression, as the union of the dependencies of its subexpressions.int
final void
Compute the static properties.final Expression
doPromotion
(Expression subexpression, PromotionOffer offer) Promote a subexpression if possible, and if the expression was changed, carry out housekeeping to reset the static properties and correct the parent pointers in the treeprotected void
dynamicError
(String message, String code, XPathContext context) Method used in subclasses to signal a dynamic errorboolean
effectiveBooleanValue
(XPathContext context) Get the effective boolean value of the expression.evaluateAsString
(XPathContext context) Evaluate an expression as a String.evaluateItem
(XPathContext context) Evaluate an expression as a single item.int
Determine the static cardinality of the expression.int
Get the column number of the expressionprotected int
Get the type of this expression for use in tracing and diagnosticsint
Determine which aspects of the context the expression depends on.Get the executable containing this expressionint
Get the host language (XSLT, XQuery, XPath) used to implement the code in this containerint
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().Get InstructionInfo for this expressionint
Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.int
Get the line number of the expressionfinal int
Get the location ID of the expressionGet the LocationProvider allowing location identifiers to be resolved.Get the expression that immediately contains this expression.final String
Get the publicId of the module containing the expression (to satisfy the SourceLocator interface)int[]
Get the local variables (identified by their slot numbers) on which this expression depends.final int
Get the static properties of this expression (other than its type).Get the systemId of the module containing the expressionboolean
Diagnostic method: search the tree for an expression whose parent expression is incorrectly setiterate
(XPathContext context) Return an Iterator to iterate over the values of a sequence.Get the immediate sub-expressions of this expression.boolean
markTailFunctionCalls
(int nameCode, int arity) Mark tail-recursive calls on stylesheet functions.void
process
(XPathContext context) Process the instruction, without returning any tail callspromote
(PromotionOffer offer) Offer promotion for this subexpression.boolean
replaceSubExpression
(Expression original, Expression replacement) Replace one subexpression by a replacement subexpressionfinal void
Reset the static properties.void
setLocationId
(int id) Set the location ID on an expression.void
setParentExpression
(Container parent) static void
setParentExpression
(Expression child, Container parent) simplify
(StaticContext env) Simplify an expression.void
suppressValidation
(int validationMode) Suppress validation on contained element constructors, on the grounds that the parent element is already performing validation.protected void
typeError
(String message, String errorCode, XPathContext context) Method used in subclasses to signal a runtime type errorMethods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface net.sf.saxon.expr.Expression
display, getItemType, optimize, typeCheck
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Field Details
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staticProperties
protected int staticProperties -
locationId
protected int locationId
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Constructor Details
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ComputedExpression
public ComputedExpression()
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Method Details
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getParentExpression
Get the expression that immediately contains this expression. This method returns null for an outermost expression; it also return null in the case of literal values. For an XPath expression occurring within an XSLT stylesheet, this method returns the XSLT instruction containing the XPath expression.- Specified by:
getParentExpression
in interfaceExpression
- Returns:
- the expression that contains this expression, if known; return null if there is no containing expression or if the containing expression is unknown.
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setParentExpression
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setParentExpression
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adoptChildExpression
Set up a parent-child relationship between this expression and a given child expression.Note: many calls on this method are now redundant, but are kept in place for "belt-and-braces" reasons. The rule is that an implementation of simplify(), typeCheck(), or optimize() that returns a value other than "this" is required to set the location information and parent pointer in the new child expression. However, in the past this was often left to the caller, which did it by calling this method, either unconditionally on return from one of these methods, or after testing that the returned object was not the same as the original.
- Parameters:
child
- the child expression
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getImplementationMethod
public int getImplementationMethod()An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.- Specified by:
getImplementationMethod
in interfaceExpression
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setLocationId
public void setLocationId(int id) Set the location ID on an expression. -
getLocationId
public final int getLocationId()Get the location ID of the expression -
getLineNumber
public int getLineNumber()Get the line number of the expression- Specified by:
getLineNumber
in interfaceSourceLocator
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getColumnNumber
public int getColumnNumber()Get the column number of the expression- Specified by:
getColumnNumber
in interfaceSourceLocator
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getSystemId
Get the systemId of the module containing the expression- Specified by:
getSystemId
in interfaceSourceLocator
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getPublicId
Get the publicId of the module containing the expression (to satisfy the SourceLocator interface)- Specified by:
getPublicId
in interfaceSourceLocator
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getExecutable
Get the executable containing this expression- Specified by:
getExecutable
in interfaceContainer
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getLocationProvider
Get the LocationProvider allowing location identifiers to be resolved.- Specified by:
getLocationProvider
in interfaceContainer
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simplify
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.- Specified by:
simplify
in interfaceExpression
- Parameters:
env
- the static context- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
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promote
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.- Specified by:
promote
in interfaceExpression
- 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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doPromotion
public final Expression doPromotion(Expression subexpression, PromotionOffer offer) throws XPathException Promote a subexpression if possible, and if the expression was changed, carry out housekeeping to reset the static properties and correct the parent pointers in the tree- Throws:
XPathException
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getSpecialProperties
public final int getSpecialProperties()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.- Specified by:
getSpecialProperties
in interfaceExpression
- Returns:
- a set of flags indicating static properties of this expression
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computeStaticProperties
public final void computeStaticProperties()Compute the static properties. This should only be done once for each expression. -
resetStaticProperties
public final void resetStaticProperties()Reset the static properties. This should be done whenever the expression is changed in a way that might affect the properties. It causes the properties to be recomputed next time they are needed. -
computeCardinality
protected abstract int computeCardinality() -
computeSpecialProperties
public int computeSpecialProperties() -
getCardinality
public int getCardinality()Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.- Specified by:
getCardinality
in interfaceExpression
- Returns:
- one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).
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getDependencies
public int getDependencies()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. The default implementation combines the intrinsic dependencies of this expression with the dependencies of the subexpressions, computed recursively. This is overridden for expressions such as FilterExpression where a subexpression's dependencies are not necessarily inherited by the parent expression.- Specified by:
getDependencies
in interfaceExpression
- Returns:
- a set of bit-significant flags identifying the dependencies of the expression
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computeDependencies
public int computeDependencies()Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.- Returns:
- the depencies, as a bit-mask
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getIntrinsicDependencies
public int getIntrinsicDependencies()Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions. For example, position() has an intrinsic dependency on the context position, while (position()+1) does not. The default implementation of the method returns 0, indicating "no dependencies".- Returns:
- a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
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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.- Specified by:
iterateSubExpressions
in interfaceExpression
- Returns:
- an iterator containing the sub-expressions of this expression
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replaceSubExpression
Replace one subexpression by a replacement subexpression- Specified by:
replaceSubExpression
in interfaceContainer
- Parameters:
original
- the original subexpressionreplacement
- the replacement subexpression- Returns:
- true if the original subexpression is found
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suppressValidation
public void suppressValidation(int validationMode) Suppress validation on contained element constructors, on the grounds that the parent element is already performing validation. The default implementation does nothing. -
checkPermittedContents
public void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.- Specified by:
checkPermittedContents
in interfaceExpression
- Parameters:
parentType
- The schema typeenv
- the static contextwhole
- true if this expression is expected to make the whole content of the type, false if it is expected to make up only a part- Throws:
XPathException
- if the expression doesn't match the required content type
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markTailFunctionCalls
public boolean markTailFunctionCalls(int nameCode, int arity) Mark tail-recursive calls on stylesheet functions. For most expressions, this does nothing.- Returns:
- true if a tail recursive call was found and if this call accounts for the whole of the value.
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getSlotsUsed
public int[] getSlotsUsed()Get the local variables (identified by their slot numbers) on which this expression depends. Should only be called if the caller has established that there is a dependency on local variables. -
evaluateItem
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 interfaceExpression
- 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
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evaluateAsString
Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.- Specified by:
evaluateAsString
in interfaceExpression
- Parameters:
context
- The context in which the expression is to be evaluated- Returns:
- the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".
- Throws:
XPathException
- if any dynamic error occurs evaluating the expressionClassCastException
- if the result type of the expression is not xs:string?
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iterate
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 interfaceExpression
- Parameters:
context
- supplies the context for evaluation- 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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effectiveBooleanValue
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.- Specified by:
effectiveBooleanValue
in interfaceExpression
- 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
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process
Process the instruction, without returning any tail calls- Specified by:
process
in interfaceExpression
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
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dynamicError
Method used in subclasses to signal a dynamic error- Throws:
DynamicError
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typeError
protected void typeError(String message, String errorCode, XPathContext context) throws DynamicError Method used in subclasses to signal a runtime type error- Throws:
DynamicError
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getInstructionInfo
Get InstructionInfo for this expression- Specified by:
getInstructionInfo
in interfaceInstructionInfoProvider
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getConstructType
protected int getConstructType()Get the type of this expression for use in tracing and diagnostics- Returns:
- the type of expression, as enumerated in class
Location
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hasBadParentPointer
public boolean hasBadParentPointer()Diagnostic method: search the tree for an expression whose parent expression is incorrectly set -
getHostLanguage
public int getHostLanguage()Get the host language (XSLT, XQuery, XPath) used to implement the code in this container- Specified by:
getHostLanguage
in interfaceContainer
- Returns:
- typically
Configuration.XSLT
orConfiguration.XQUERY
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