Class CastExpression

All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, Locator

public final class CastExpression extends UnaryExpression
Cast Expression: implements "cast as data-type ( expression )". It also allows an internal cast, which has the same semantics as a user-requested cast, but maps an empty sequence to an empty sequence.
See Also:
  • Constructor Details

    • CastExpression

      public CastExpression(Expression source, AtomicType target, boolean allowEmpty)
      Create a cast expression
      Parameters:
      source - expression giving the value to be converted
      target - the type to which the value is to be converted
      allowEmpty - true if the expression allows an empty sequence as input, producing an empty sequence as output. If false, an empty sequence is a type error.
  • Method Details

    • isPossibleCast

      public static boolean isPossibleCast(int source, int target)
      Determine whether casting from a source type to a target type is possible
      Parameters:
      source - a primitive type (one that has an entry in the casting table)
      target - another primitive type
      Returns:
      true if the entry in the casting table is either "Y" (casting always succeeds) or "M" (casting allowed but may fail for some values)
    • getTargetPrimitiveType

      public AtomicType getTargetPrimitiveType()
      Get the primitive base type of the target type of the cast
      Returns:
      the primitive type of the target type
    • getTargetType

      public AtomicType getTargetType()
      Get the target type (the result type)
      Returns:
      the target type
    • allowsEmpty

      public boolean allowsEmpty()
      Ask whether the expression accepts an empty sequence as input (producing an empty sequence as output)
      Returns:
      true if an empty sequence is accepted
    • targetIsDerived

      public boolean targetIsDerived()
      Ask whether the target type is a derived type (not a primitive type)
      Returns:
      true if the target type is a derived type
    • isUpCast

      public boolean isUpCast()
      Ask whether this is a cast to a supertype of the original type
      Returns:
      true if this is an upcast. This means the value stays unchanged and only the type label changes
    • simplify

      public Expression simplify(ExpressionVisitor visitor) throws XPathException
      Simplify the expression
      Overrides:
      simplify in class UnaryExpression
      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, ItemType contextItemType) throws XPathException
      Type-check the expression
      Overrides:
      typeCheck in class UnaryExpression
      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)
    • computeCardinality

      public int computeCardinality()
      Get the static cardinality of the expression
      Overrides:
      computeCardinality in class UnaryExpression
      Returns:
      the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Get the static type of the expression
      Overrides:
      getItemType in class UnaryExpression
      Parameters:
      th - the type hierarchy cache
      Returns:
      the item type of the items in the result sequence, insofar as this is known statically.
    • computeSpecialProperties

      public int computeSpecialProperties()
      Determine the special properties of this expression
      Overrides:
      computeSpecialProperties in class UnaryExpression
      Returns:
      StaticProperty.NON_CREATIVE.
    • 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
    • evaluateItem

      public Item evaluateItem(XPathContext context) throws XPathException
      Evaluate the expression
      Specified by:
      evaluateItem in interface EvaluableItem
      Overrides:
      evaluateItem in class 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
    • equals

      public boolean equals(Object other)
      Is this expression the same as another expression?
      Overrides:
      equals in class UnaryExpression
    • toString

      public String toString()
      The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
      Overrides:
      toString in class UnaryExpression
    • explain

      public void explain(ExpressionPresenter out)
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Overrides:
      explain in class UnaryExpression
      Parameters:
      out - the expression presenter used to display the structure
    • castStringToQName

      public static AtomicValue castStringToQName(CharSequence operand, AtomicType targetType, StaticContext env) throws XPathException
      Evaluate the "pseudo-cast" of a string literal to a QName or NOTATION value. This can only happen at compile time
      Parameters:
      operand - the value to be converted
      targetType - the type to which it is to be converted
      env - the static context
      Returns:
      the QName or NOTATION value that results from casting the string to a QName. This will either be a QNameValue or a derived AtomicValue derived from QName or NOTATION
      Throws:
      XPathException