Class Choose

    • Constructor Detail

      • Choose

        public Choose​(Expression[] conditions,
                      Expression[] actions)
        Construct an xsl:choose instruction
        Parameters:
        conditions - the conditions to be tested, in order
        actions - the actions to be taken when the corresponding condition is true
    • Method Detail

      • makeConditional

        public static Expression makeConditional​(Expression condition,
                                                 Expression thenExp,
                                                 Expression elseExp)
        Make a simple conditional expression (if (condition) then (thenExp) else (elseExp)
        Parameters:
        condition - the condition to be tested
        thenExp - the expression to be evaluated if the condition is true
        elseExp - the expression to be evaluated if the condition is false
        Returns:
        the expression
      • makeConditional

        public static Expression makeConditional​(Expression condition,
                                                 Expression thenExp)
        Make a simple conditional expression (if (condition) then (thenExp) else ()
        Parameters:
        condition - the condition to be tested
        thenExp - the expression to be evaluated if the condition is true
        Returns:
        the expression
      • isSingleBranchChoice

        public static boolean isSingleBranchChoice​(Expression exp)
        Test whether an expression is a single-branch choose, that is, an expression of the form if (condition) then exp else ()
        Parameters:
        exp - the expression to be tested
        Returns:
        true if the expression is a choose expression and there is only one condition, so that the expression returns () if this condition is false
      • getConditions

        public Expression[] getConditions()
        Get the array of conditions to be tested
        Returns:
        the array of condition expressions
      • getActions

        public Expression[] getActions()
        Get the array of actions to be performed
        Returns:
        the array of expressions to be evaluated when the corresponding condition is true
      • getInstructionNameCode

        public int getInstructionNameCode()
        Get the name of this instruction for diagnostic and tracing purposes We assume that if there was only one condition then it was an xsl:if; this is not necessarily so, but it's adequate for tracing purposes.
        Overrides:
        getInstructionNameCode in class Instruction
        Returns:
        a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace
      • simplify

        public Expression simplify​(ExpressionVisitor visitor)
                            throws XPathException
        Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).
        Specified by:
        simplify in class Instruction
        Parameters:
        visitor - expression visitor object
        Returns:
        the simplified expression
        Throws:
        XPathException - if an error is discovered during expression rewriting
      • typeCheck

        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 parent pointer and 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)
      • implementsStaticTypeCheck

        public boolean implementsStaticTypeCheck()
        Determine whether this expression implements its own method for static type checking
        Overrides:
        implementsStaticTypeCheck in class Expression
        Returns:
        true - this expression has a non-trivial implementation of the staticTypeCheck() method
      • staticTypeCheck

        public Expression staticTypeCheck​(SequenceType req,
                                          boolean backwardsCompatible,
                                          RoleLocator role,
                                          ExpressionVisitor visitor)
                                   throws XPathException
        Static type checking for conditional expressions is delegated to the expression itself, and is performed separately on each branch of the conditional, so that dynamic checks are added only on those branches where the check is actually required. This also results in a static type error if any branch is incapable of delivering a value of the required type. One reason for this approach is to avoid doing dynamic type checking on a recursive function call as this prevents tail-call optimization being used.
        Overrides:
        staticTypeCheck in class Expression
        Parameters:
        req - the required type
        backwardsCompatible - true if backwards compatibility mode applies
        role - the role of the expression in relation to the required type
        visitor - an expression visitor
        Returns:
        the expression after type checking (perhaps augmented with dynamic type checking code)
        Throws:
        XPathException - if failures occur, for example if the static type of one branch of the conditional is incompatible with the required type
      • optimize

        public Expression optimize​(ExpressionVisitor visitor,
                                   ItemType 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)
      • 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
      • checkForUpdatingSubexpressions

        public void checkForUpdatingSubexpressions()
                                            throws XPathException
        Check to ensure that this expression does not contain any 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 updateing subexpression
      • 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
      • markTailFunctionCalls

        public int markTailFunctionCalls​(StructuredQName qName,
                                         int arity)
        Mark tail-recursive calls on functions. For most expressions, this does nothing.
        Overrides:
        markTailFunctionCalls in class Expression
        Parameters:
        qName - the name of the function
        arity - the arity (number of parameters) of the function
        Returns:
        0 if no tail call was found; 1 if a tail call on a different function was found; 2 if a tail recursive call was found and if this call accounts for the whole of the value.
      • 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 - Type hierarchy cache
        Returns:
        the static item type of the instruction
      • computeCardinality

        public int computeCardinality()
        Compute the cardinality of the sequence returned by evaluating this instruction
        Overrides:
        computeCardinality in class Instruction
        Returns:
        the static cardinality
      • computeSpecialProperties

        public int computeSpecialProperties()
        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:
        computeSpecialProperties in class Instruction
        Returns:
        a set of flags indicating static properties of this expression
      • createsNewNodes

        public final boolean createsNewNodes()
        Determine whether this instruction creates new nodes. This implementation returns true if any of the "actions" creates new nodes. (Nodes created by the conditions can't contribute to the result).
        Overrides:
        createsNewNodes in class Instruction
        Returns:
        true if the instruction creates new nodes (or if it can't be proved that it doesn't)
      • iterateSubExpressions

        public java.util.Iterator iterateSubExpressions()
        Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)
        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
      • 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.
        Overrides:
        checkPermittedContents in class Expression
        Parameters:
        parentType - the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this type
        env - the static context
        whole - if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content
        Throws:
        XPathException - if the value delivered by this expression cannot be part of the content model of the given type
      • addToPathMap

        public PathMap.PathMapNodeSet addToPathMap​(PathMap pathMap,
                                                   PathMap.PathMapNodeSet pathMapNodeSet)
        Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

        The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

        Overrides:
        addToPathMap in class Expression
        Parameters:
        pathMap - the PathMap to which the expression should be added
        pathMapNodeSet - the set of PathMap nodes to which the paths from this expression should be appended
        Returns:
        the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.
      • 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
      • processLeavingTail

        public TailCall processLeavingTail​(XPathContext context)
                                    throws XPathException
        Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.
        Specified by:
        processLeavingTail in interface TailCallReturner
        Specified by:
        processLeavingTail in class Instruction
        Parameters:
        context - the dynamic context of this transformation
        Returns:
        a TailCall, if the chosen branch ends with a call of call-template or apply-templates. It is the caller's responsibility to execute such a TailCall. If there is no TailCall, returns null.
        Throws:
        XPathException - if any non-recoverable dynamic error occurs
      • 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 EvaluableItem
        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 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 relies on the process() method: it "pushes" the results of the instruction to a sequence in memory, and then iterates over this in-memory sequence. In principle instructions should implement a pipelined iterate() method that avoids the overhead of intermediate storage.
        Specified by:
        iterate in interface SequenceIterable
        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
      • iterateEvents

        public EventIterator iterateEvents​(XPathContext context)
                                    throws XPathException
        Deliver the result of the expression as a sequence of events.

        The events (of class PullEvent) are either complete items, or one of startElement, endElement, startDocument, or endDocument, known as semi-nodes. The stream of events may also include a nested EventIterator. If a start-end pair exists in the sequence, then the events between this pair represent the content of the document or element. The content sequence will have been processed to the extent that any attribute and namespace nodes in the content sequence will have been merged into the startElement event. Namespace fixup will have been performed: that is, unique prefixes will have been allocated to element and attribute nodes, and all namespaces will be declared by means of a namespace node in the startElement event or in an outer startElement forming part of the sequence. However, duplicate namespaces may appear in the sequence.

        The content of an element or document may include adjacent or zero-length text nodes, atomic values, and nodes represented as nodes rather than broken down into events.

        Overrides:
        iterateEvents in class Expression
        Parameters:
        context - The dynamic evaluation context
        Returns:
        the result of the expression as an iterator over a sequence of PullEvent objects
        Throws:
        XPathException - if a dynamic error occurs during expression evaluation
      • 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