Package net.sf.saxon.expr.instruct

Class Block

  • All Implemented Interfaces:
    ExportAgent, Locatable, IdentityComparable, Traceable
    public class Block
extends Instruction
    An expression that delivers the concatenation of the results of its subexpressions. This may represent an XSLT sequence constructor, or an XPath/XQuery expression of the form (a,b,c,d).

    • Constructor Detail

      • Block

        public Block​(Expression[] children)
        Create a block, supplying its child expressions
        Parameters:
        children - the child expressions in order

    • Method Detail

      • isInstruction

        public boolean isInstruction()
        Description copied from class: Expression
        Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs, typically XPath expressions (but also things like attribute constructors on a literal result element, references to attribute sets, etc. However, an XPath expression within a text value template in a text node of an XSLT stylesheet is treated as an instruction. In a non-XSLT environment (such as XQuery) this property has no meaning and its setting is undefined.
        Overrides:
        isInstruction in class Instruction
        Returns:
        true if this construct originates as an XSLT instruction

      • size

        public int size()
        Get the number of children
        Returns:
        the number of child subexpressions

      • operands

        public java.lang.Iterable<Operand> operands()
        Description copied from class: Expression
        Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.

        If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

        Specified by:
        operands in class Instruction
        Returns:
        an iterator containing the sub-expressions of this expression

      • hasVariableBinding

        public boolean hasVariableBinding​(Binding binding)
        Ask whether this expression is, or contains, the binding of a given variable
        Overrides:
        hasVariableBinding in class Expression
        Parameters:
        binding - the variable binding
        Returns:
        true if this expression is the variable binding (for example a ForExpression or LetExpression) or if it is a FLWOR expression that binds the variable in one of its clauses.

      • 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. The list is effectively copied; subsequent changes to the contents of the list have no effect.
        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

      • 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.

      • getOperanda

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

      • computeSpecialProperties

        protected 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

      • implementsStaticTypeCheck

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

      • staticTypeCheck

        public Expression staticTypeCheck​(SequenceType req,
                                  boolean backwardsCompatible,
                                  java.util.function.Supplier<RoleDiagnostic> roleSupplier,
                                  ExpressionVisitor visitor)
                           throws XPathException
        Static type checking for let expressions is delegated to the child expressions, to allow further delegation to the branches of a conditional
        Overrides:
        staticTypeCheck in class Expression
        Parameters:
        req - the required type
        backwardsCompatible - true if backwards compatibility mode applies
        roleSupplier - 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

      • neverReturnsTypedNodes

        public static boolean neverReturnsTypedNodes​(Instruction insn,
                                             TypeHierarchy th)
        Determine whether the block includes any instructions that might return nodes with a type annotation
        Parameters:
        insn - the instruction (for example this block)
        th - the type hierarchy cache
        Returns:
        true if any expression in the block can return type-annotated nodes

      • mergeAdjacentTextInstructions

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

      • copy

        public Expression copy​(RebindingMap rebindings)
        Copy an expression. This makes a deep copy.
        Specified by:
        copy in class Expression
        Parameters:
        rebindings - Variables that need to be re-bound
        Returns:
        the copy of the original expression

      • getItemType

        public final ItemType getItemType()
        Determine the data type of the items returned by this expression
        Overrides:
        getItemType in class Instruction
        Returns:
        the data type

      • getStaticUType

        public UType getStaticUType​(UType contextItemType)
        Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
        Overrides:
        getStaticUType in class Expression
        Parameters:
        contextItemType - the static type of the context item
        Returns:
        the static item type of the expression according to the XSLT 3.0 defined rules

      • computeCardinality

        protected int computeCardinality()
        Determine the cardinality of the expression
        Overrides:
        computeCardinality in class Instruction
        Returns:
        the static cardinality

      • mayCreateNewNodes

        public final boolean mayCreateNewNodes()
        Determine whether this instruction creates new nodes. This implementation returns true if any child instruction returns true.
        Overrides:
        mayCreateNewNodes in class Instruction
        Returns:
        true if the instruction creates new nodes under some input conditions (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()
                    throws XPathException
        Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.
        Overrides:
        simplify in class Expression
        Returns:
        the simplified expression (or the original if unchanged, or if modified in-situ)
        Throws:
        XPathException - if an error is discovered during expression rewriting

      • isCandidateForSharedAppend

        public boolean isCandidateForSharedAppend()
        Determine whether the block is a candidate for evaluation using a "shared append expression" where the result of the evaluation is a sequence implemented as a list of subsequences
        Returns:
        true if the block is a candidate for "shared append" processing

      • typeCheck

        public Expression typeCheck​(ExpressionVisitor visitor,
                            ContextItemStaticInfo contextInfo)
                     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.

        Overrides:
        typeCheck in class Expression
        Parameters:
        visitor - an expression visitor
        contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.
        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,
                           ContextItemStaticInfo contextInfo)
                    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
        contextInfo - 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,
                                   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
        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

      • export

        public void export​(ExpressionPresenter out)
            throws XPathException
        Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
        Specified by:
        export in interface ExportAgent
        Specified by:
        export in class Expression
        Parameters:
        out - the expression presenter used to display the structure
        Throws:
        XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

      • toShortString

        public java.lang.String toShortString()
        Description copied from class: Expression
        Produce a short string identifying the expression for use in error messages
        Overrides:
        toShortString in class Expression
        Returns:
        a short string, sufficient to identify the expression

      • iterate

        public SequenceIterator 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

      • getStreamerName

        public java.lang.String getStreamerName()
        Description copied from class: Expression
        Get the (partial) name of a class that supports streaming of this kind of expression
        Overrides:
        getStreamerName in class Expression
        Returns:
        the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class

      • getElaborator

        public Elaborator getElaborator()
        Make an elaborator for this expression
        Overrides:
        getElaborator in class Expression
        Returns:
        a suitable elaborator