Package net.sf.saxon.expr.instruct

Class Block

    • Constructor Detail

      • Block

        public Block()
        Create an empty block

    • Method Detail

      • makeBlock

        public static Expression makeBlock​(Expression e1,
                                   Expression e2)
        Static factory method to create a block. If one of the arguments is already a block, the contents will be merged into a new composite block
        Parameters:
        e1 - the first subexpression (child) of the block
        e2 - the second subexpression (child) of the block
        Returns:
        a Block containing the two subexpressions, and if either of them is a block, it will have been collapsed to create a flattened sequence

      • makeBlock

        public static Expression makeBlock​(java.util.List<Expression> list)
        Static factory method to create a block from a list of expressions
        Parameters:
        list - the list of expressions making up this block. The members of the List must be instances of Expression
        Returns:
        a Block containing the two subexpressions, and if either of them is a block, it will have been collapsed to create a flattened sequence

      • setChildren

        public void setChildren​(Expression[] children)
        Set the children of this instruction
        Parameters:
        children - The instructions that are children of this instruction

      • getExpressionName

        public java.lang.String getExpressionName()
        Description copied from class: Instruction
        Get a name identifying the kind of expression, in terms meaningful to a user.
        Overrides:
        getExpressionName in class Instruction
        Returns:
        a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

      • getChildren

        public Expression[] getChildren()
        Get the children of this instruction
        Returns:
        the children of this instruction, as an array of Instruction objects. May return a zero-length array if there are no children

      • computeSpecialProperties

        public int computeSpecialProperties()
        Description copied from class: Instruction
        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

      • mergeAdjacentTextInstructions

        public Expression mergeAdjacentTextInstructions()
        Merge any adjacent instructions that create literal text nodes
        Returns:
        the expression after merging literal text instructions

      • 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

      • 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

      • getItemType

        public final ItemType getItemType​(TypeHierarchy th)
        Determine the data type of the items returned by this expression
        Overrides:
        getItemType in class Instruction
        Parameters:
        th - the type hierarchy cache
        Returns:
        the data type

      • getCardinality

        public final int getCardinality()
        Determine the cardinality of the expression
        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).

      • createsNewNodes

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

      • 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

      • 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

      • 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)

      • 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

      • 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
        Description copied from class: Instruction
        ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.
        Specified by:
        processLeavingTail in interface TailCallReturner
        Specified by:
        processLeavingTail in class Instruction
        Parameters:
        context - The dynamic context of the transformation, giving access to the current node, the current variables, etc.
        Returns:
        null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
        Throws:
        XPathException - if a dynamic error occurs during the evaluation of the instruction

      • iterate

        public SequenceIterator<? extends Item> iterate​(XPathContext context)
                                         throws XPathException
        Iterate over the results of all the child expressions
        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

      • 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