Class ComputedExpression

    • Field Detail

      • staticProperties

        protected int staticProperties
      • locationId

        protected int locationId
    • Constructor Detail

      • ComputedExpression

        public ComputedExpression()
    • Method Detail

      • getParentExpression

        public Container 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 interface Expression
        Returns:
        the expression that contains this expression, if known; return null if there is no containing expression or if the containing expression is unknown.
      • setParentExpression

        public void setParentExpression​(Container parent)
      • setParentExpression

        public static void setParentExpression​(Expression child,
                                               Container parent)
      • adoptChildExpression

        public void adoptChildExpression​(Expression child)
        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
      • 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 interface Expression
      • 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 interface javax.xml.transform.SourceLocator
      • getColumnNumber

        public int getColumnNumber()
        Get the column number of the expression
        Specified by:
        getColumnNumber in interface javax.xml.transform.SourceLocator
      • getSystemId

        public java.lang.String getSystemId()
        Get the systemId of the module containing the expression
        Specified by:
        getSystemId in interface javax.xml.transform.SourceLocator
      • getPublicId

        public final java.lang.String getPublicId()
        Get the publicId of the module containing the expression (to satisfy the SourceLocator interface)
        Specified by:
        getPublicId in interface javax.xml.transform.SourceLocator
      • simplify

        public Expression simplify​(StaticContext env)
                            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 interface Expression
        Parameters:
        env - the static context
        Returns:
        the simplified expression
        Throws:
        XPathException - if an error is discovered during expression rewriting
      • promote

        public Expression promote​(PromotionOffer offer)
                           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.
        Specified by:
        promote in interface 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
      • 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
      • 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 interface Expression
        Returns:
        a set of flags indicating static properties of this expression
      • 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 interface 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 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 interface Expression
        Returns:
        a set of bit-significant flags identifying the dependencies of the expression
      • 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
      • 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
      • iterateSubExpressions

        public java.util.Iterator 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 interface 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
        Specified by:
        replaceSubExpression in interface Container
        Parameters:
        original - the original subexpression
        replacement - the replacement subexpression
        Returns:
        true if the original subexpression is found
      • 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 interface Expression
        Parameters:
        parentType - The schema type
        env - the static context
        whole - 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
      • 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.
      • 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

        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 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
      • evaluateAsString

        public java.lang.String evaluateAsString​(XPathContext context)
                                          throws XPathException
        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 interface Expression
        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 expression
        java.lang.ClassCastException - if the result type of the expression is not xs:string?
      • iterate

        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 Expression
        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
      • effectiveBooleanValue

        public boolean effectiveBooleanValue​(XPathContext context)
                                      throws XPathException
        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 interface 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
      • process

        public void process​(XPathContext context)
                     throws XPathException
        Process the instruction, without returning any tail calls
        Specified by:
        process in interface Expression
        Parameters:
        context - The dynamic context, giving access to the current node, the current variables, etc.
        Throws:
        XPathException
      • dynamicError

        protected void dynamicError​(java.lang.String message,
                                    java.lang.String code,
                                    XPathContext context)
                             throws DynamicError
        Method used in subclasses to signal a dynamic error
        Throws:
        DynamicError
      • typeError

        protected void typeError​(java.lang.String message,
                                 java.lang.String errorCode,
                                 XPathContext context)
                          throws DynamicError
        Method used in subclasses to signal a runtime type error
        Throws:
        DynamicError
      • 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
      • hasBadParentPointer

        public boolean hasBadParentPointer()
        Diagnostic method: search the tree for an expression whose parent expression is incorrectly set