Package net.sf.saxon.expr.instruct

Class TraceExpression

    • Constructor Detail

      • TraceExpression

        public TraceExpression​(Expression child)
        Create a trace expression that traces execution of a given child expression
        Parameters:
        child - the expression to be traced. This will be available to the TraceListener as the value of the "expression" property of the InstructionInfo.

    • Method Detail

      • setConstructType

        public void setConstructType​(int type)
        Set the type of construct. This will generally be a constant in class Location
        Parameters:
        type - an integer code for the type of construct being traced

      • setNamespaceResolver

        public void setNamespaceResolver​(NamespaceResolver resolver)
        Set the namespace context for the instruction being traced. This is needed if the tracelistener wants to evaluate XPath expressions in the context of the current instruction
        Parameters:
        resolver - The namespace resolver, or null if none is needed

      • getNamespaceResolver

        public NamespaceResolver getNamespaceResolver()
        Get the namespace resolver to supply the namespace context of the instruction that is being traced
        Returns:
        the namespace resolver, or null if none is in use

      • setObjectName

        public void setObjectName​(StructuredQName qName)
        Set a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc. This is used only where the name is known statically.
        Parameters:
        qName - the name of the object, or null if not applicable

      • getObjectName

        public StructuredQName getObjectName()
        Get a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc. This is used only where the name is known statically.
        Specified by:
        getObjectName in interface InstructionInfo
        Overrides:
        getObjectName in class Expression
        Returns:
        the name of the object, or null if not applicable

      • setProperty

        public void setProperty​(java.lang.String name,
                        java.lang.Object value)
        Set a named property of the instruction/expression
        Parameters:
        name - the name of the property
        value - the value of the property

      • getProperty

        public java.lang.Object getProperty​(java.lang.String name)
        Get a named property of the instruction/expression
        Specified by:
        getProperty in interface InstructionInfo
        Overrides:
        getProperty in class Expression
        Parameters:
        name - the name of the property
        Returns:
        the value of the property

      • getProperties

        public java.util.Iterator<java.lang.String> getProperties()
        Get an iterator over all the properties available. The values returned by the iterator will be of type String, and each string can be supplied as input to the getProperty() method to retrieve the value of the property.
        Specified by:
        getProperties in interface InstructionInfo
        Overrides:
        getProperties in class Expression
        Returns:
        an iterator over the properties.

      • getInstructionInfo

        public InstructionInfo getInstructionInfo()
        Get the InstructionInfo details about the construct. This is to satisfy the InstructionInfoProvider interface.
        Returns:
        the instruction details

      • getSystemId

        public java.lang.String getSystemId​(long locationId)
        Get the system identifier (that is the base URI) of the static context of the expression being traced. This returns the same result as getSystemId(), it is provided to satisfy the LocationProvider interface.
        Specified by:
        getSystemId in interface LocationProvider
        Overrides:
        getSystemId in class Expression
        Parameters:
        locationId - not used
        Returns:
        the URI of the module containing the expression

      • getLineNumber

        public int getLineNumber​(long locationId)
        Get the line number of the expression being traced. This returns the same result as getLineNumber(), it is provided to satisfy the LocationProvider interface.
        Specified by:
        getLineNumber in interface LocationProvider
        Overrides:
        getLineNumber in class Expression
        Parameters:
        locationId - not used
        Returns:
        the line number of the expression within its module

      • getColumnNumber

        public int getColumnNumber​(long locationId)
        Description copied from interface: LocationProvider
        Get the column number within the document, entity, or module containing a particular location
        Specified by:
        getColumnNumber in interface LocationProvider
        Overrides:
        getColumnNumber in class Expression
        Parameters:
        locationId - identifier of the location in question (as passed down the Receiver pipeline)
        Returns:
        the column number within the document, entity, or module, or -1 if this is not available

      • copy

        public Expression copy()
        Description copied from class: Expression
        Copy an expression. This makes a deep copy.
        Specified by:
        copy in class Expression
        Returns:
        the copy of the original expression

      • isUpdatingExpression

        public boolean isUpdatingExpression()
        Determine whether this is an updating expression as defined in the XQuery update specification
        Overrides:
        isUpdatingExpression in class Expression
        Returns:
        true if this is an updating expression

      • isVacuousExpression

        public boolean isVacuousExpression()
        Determine whether this is a vacuous expression as defined in the XQuery update specification
        Overrides:
        isVacuousExpression in class Expression
        Returns:
        true if this expression is vacuous

      • checkForUpdatingSubexpressions

        public void checkForUpdatingSubexpressions()
                                    throws XPathException
        Check to ensure that this expression does not contain any inappropriate updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.
        Overrides:
        checkForUpdatingSubexpressions in class Expression
        Throws:
        XPathException - if the expression has a non-permitted updating subexpression

      • simplify

        public Expression simplify​(ExpressionVisitor visitor)
                    throws XPathException
        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 class Instruction
        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,
                            ExpressionVisitor.ContextItemType 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.

        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,
                           ExpressionVisitor.ContextItemType 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)

      • promote

        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. This method is always called at compile time.
        Overrides:
        promote in class Instruction
        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
        parent - the parent of the subexpression
        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

      • processLeavingTail

        public TailCall processLeavingTail​(XPathContext context)
                            throws XPathException
        Execute this instruction, with the possibility of returning tail calls if there are any. This outputs the trace information via the registered TraceListener, and invokes the instruction being traced.
        Specified by:
        processLeavingTail in interface TailCallReturner
        Specified by:
        processLeavingTail in class Instruction
        Parameters:
        context - the dynamic execution context
        Returns:
        either null, or a tail call that the caller must invoke on return
        Throws:
        XPathException

      • getItemType

        public ItemType getItemType​(TypeHierarchy th)
        Get the item type of the items returned by evaluating this instruction
        Overrides:
        getItemType in class Instruction
        Parameters:
        th - the type hierarchy cache
        Returns:
        the static item type of the instruction

      • 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.
        Overrides:
        getCardinality in class Expression
        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).

      • 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 StaticProperty.DEPENDS_ON_CONTEXT_ITEM and StaticProperty.DEPENDS_ON_CURRENT_ITEM. 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.
        Overrides:
        getDependencies in class Expression
        Returns:
        a set of bit-significant flags identifying the dependencies of the expression

      • createsNewNodes

        public final boolean createsNewNodes()
        Determine whether this instruction creates new nodes.
        Overrides:
        createsNewNodes in class Instruction
        Returns:
        true if the instruction creates new nodes (or if it can't be proved that it doesn't)

      • computeDependencies

        public int computeDependencies()
        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:
        computeDependencies in class Expression
        Returns:
        a set of flags indicating static properties of this expression

      • evaluateItem

        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.
        Overrides:
        evaluateItem in class Instruction
        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

      • iterate

        public SequenceIterator<Item> 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.
        Overrides:
        iterate in class Instruction
        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

      • iterateSubExpressions

        public java.util.Iterator<Expression> iterateSubExpressions()
        Description copied from class: Expression
        Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.
        Overrides:
        iterateSubExpressions in class Expression
        Returns:
        an iterator containing the sub-expressions of this expression

      • 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

      • getChildExpression

        public Expression getChildExpression()

      • getInstructionNameCode

        public int getInstructionNameCode()
        Description copied from class: Instruction
        Get the namecode of the instruction for use in diagnostics
        Overrides:
        getInstructionNameCode in class Instruction
        Returns:
        a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

      • explain

        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
        Parameters:
        out - the expression presenter used to display the structure

      • evaluatePendingUpdates

        public void evaluatePendingUpdates​(XPathContext context,
                                   PendingUpdateList pul)
                            throws XPathException
        Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException
        Overrides:
        evaluatePendingUpdates in class Expression
        Parameters:
        context - the XPath dynamic evaluation context
        pul - the pending update list to which the results should be written
        Throws:
        XPathException - if evaluation fails