Package net.sf.saxon.expr.instruct

Class Block

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.instruct.Instruction
net.sf.saxon.expr.instruct.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 Details

    • Block

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

  • Method Details

    • 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 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(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 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, 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 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

    • 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. This implementation provides both iterate() and process() methods natively.
      Overrides:
      getImplementationMethod in class Instruction
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

    • 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 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