Class PatternSponsor

java.lang.Object
net.sf.saxon.pattern.PatternSponsor
All Implemented Interfaces:
Serializable, Expression

public class PatternSponsor extends Object implements Expression
The PatternSponsor class allows a Pattern to be treated like an expression. Although patterns are not evaluated at run-time in the same way as expressions, they need to be manipulated in much the same way as expressions at compile time: for example variables need to be bound, dependencies need to be analyzed, and so on. This is especially true of patterns appearing in the xsl:number and xsl:for-each-group instructions (less so for the more common match patterns in xsl:template).

This class implements the Expression interface, so that an Expression can have a PatternSponsor as a subexpression; it wraps a Pattern.

A Pattern is treated as a boolean expression that returns true if the pattern matches the context node. However, it is not currently evaluated in that way.

See Also:
  • Constructor Details

    • PatternSponsor

      public PatternSponsor(Pattern pattern)
  • Method Details

    • getPattern

      public Pattern getPattern()
      Get the wrapped pattern
    • 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
    • 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:
      StaticError - if an error is discovered during expression rewriting
      XPathException
    • optimize

      public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException
      Perform optimisation of an expression and its subexpressions.

      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.

      Specified by:
      optimize in interface Expression
      Parameters:
      opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.
      env - the static context of the expression
      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:
      StaticError - if an error is discovered during this phase (typically a type error)
      XPathException
    • typeCheck

      public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
      Perform type checking of an expression and its subexpressions.

      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.

      Specified by:
      typeCheck in interface Expression
      Parameters:
      env - the static context of the expression
      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:
      StaticError - if an error is discovered during this phase (typically a type error)
      XPathException
    • 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
    • getSpecialProperties

      public 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
    • 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.

      This method should always return a result, though it may be the best approximation that is available at the time.

      Specified by:
      getCardinality in interface Expression
      Returns:
      one of the values StaticProperty.ALLOWS_ONE, StaticProperty.ALLOWS_ZERO_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.EMPTY.
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

      This method should always return a result, though it may be the best approximation that is available at the time.

      Specified by:
      getItemType in interface Expression
      Parameters:
      th -
      Returns:
      a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)
    • 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 StaticProperty.DEPENDS_ON_CONTEXT_ITEM and StaticProperty.DEPENDS_ON_CURRENT_ITEM. 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
    • iterateSubExpressions

      public 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
    • getParentExpression

      public Container getParentExpression()
      Get the container 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.
    • 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
    • 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
    • evaluateAsString

      public 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
      ClassCastException - if the result type of the expression is not xs:string?
    • 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
    • display

      public void display(int level, PrintStream out, Configuration config)
      Diagnostic print of expression structure. The expression is written to the System.err output stream
      Specified by:
      display in interface Expression
      Parameters:
      level - indentation level for this expression
      out - Output destination
      config -
    • checkPermittedContents

      public void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException
      Check statically that the results of the expression are capable of constructing the content of a given schema type.
      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