Package net.sf.saxon.expr.parser

Class TypeChecker

java.lang.Object
net.sf.saxon.expr.parser.TypeChecker
Direct Known Subclasses:
TypeChecker10
public class TypeChecker extends Object
This class provides Saxon's type checking capability. It contains a method, staticTypeCheck, which is called at compile time to perform type checking of an expression.

  • Constructor Details

    • TypeChecker

      public TypeChecker()

  • Method Details

    • staticTypeCheck

      public Expression staticTypeCheck(Expression supplied, SequenceType req, Supplier<RoleDiagnostic> roleSupplier, ExpressionVisitor visitor) throws XPathException
      Check an expression against a required type, modifying it if necessary.

      This method takes the supplied expression and checks to see whether it is known statically to conform to the specified type. There are three possible outcomes. If the static type of the expression is a subtype of the required type, the method returns the expression unchanged. If the static type of the expression is incompatible with the required type (for example, if the supplied type is integer and the required type is string) the method throws an exception (this results in a compile-time type error being reported). If the static type is a supertype of the required type, then a new expression is constructed that evaluates the original expression and checks the dynamic type of the result; this new expression is returned as the result of the method.

      The rules applied are those for function calling in XPath, that is, the rules that the argument of a function call must obey in relation to the signature of the function. Some contexts require slightly different rules (for example, operands of polymorphic operators such as "+"). In such cases this method cannot be used.

      Note that this method does not do recursive type-checking of the sub-expressions.

      Parameters:
      supplied - The expression to be type-checked
      req - The required type for the context in which the expression is used
      roleSupplier - Information about the role of the subexpression within the containing expression, used to provide useful error messages
      visitor - An expression visitor
      Returns:
      The original expression if it is type-safe, or the expression wrapped in a run-time type checking expression if not.
      Throws:
      XPathException - if the supplied type is statically inconsistent with the required type (that is, if they have no common subtype)

    • makePromotingConverter

      public static Converter makePromotingConverter(ItemType suppliedItemType, int requiredType, ConversionRules rules, boolean allow40)
      Make an expression that performs type promotion on a supplied sequence
      Parameters:
      suppliedItemType - the inferred type of the supplied value
      requiredType - the required type, the target of promotion
      rules - the conversion rules
      allow40 - true if XPath 4.0 is enabled
      Returns:
      the promoting converter, if available for the required type, or null. Note that promoting converters not only implement type promotion (for example from decimal to double) but also perform conversion of untypedAtomic values to the target type.

    • makeArithmeticExpression

      public Expression makeArithmeticExpression(Expression lhs, int operator, Expression rhs)

    • makeGeneralComparison

      public Expression makeGeneralComparison(Expression lhs, int operator, Expression rhs)

    • processValueOf

      public Expression processValueOf(Expression select, Configuration config)

    • strictTypeCheck

      public static Expression strictTypeCheck(Expression supplied, SequenceType req, Supplier<RoleDiagnostic> roleSupplier, StaticContext env) throws XPathException
      Check an expression against a required type, modifying it if necessary. This is a variant of the method staticTypeCheck(net.sf.saxon.expr.Expression, net.sf.saxon.value.SequenceType, java.util.function.Supplier<net.sf.saxon.expr.parser.RoleDiagnostic>, net.sf.saxon.expr.parser.ExpressionVisitor) used for expressions that declare variables in XQuery. In these contexts, conversions such as numeric type promotion and atomization are not allowed.
      Parameters:
      supplied - The expression to be type-checked
      req - The required type for the context in which the expression is used
      roleSupplier - Information about the role of the subexpression within the containing expression, used to provide useful error messages
      env - The static context containing the types being checked. At present this is used only to locate a NamePool
      Returns:
      The original expression if it is type-safe, or the expression wrapped in a run-time type checking expression if not.
      Throws:
      XPathException - if the supplied type is statically inconsistent with the required type (that is, if they have no common subtype)

    • testConformance

      public static XPathException testConformance(Sequence val, SequenceType requiredType, XPathContext context) throws XPathException
      Test whether a given value conforms to a given type
      Parameters:
      val - the value
      requiredType - the required type
      context - XPath dynamic context
      Returns:
      an XPathException describing the error condition if the value doesn't conform; or null if it does.
      Throws:
      XPathException - if a failure occurs reading the value

    • ebvError

      public static XPathException ebvError(Expression exp, TypeHierarchy th)
      Test whether a given expression is capable of returning a value that has an effective boolean value.
      Parameters:
      exp - the given expression
      th - the type hierarchy cache
      Returns:
      null if the expression is OK (optimistically), an exception object if not