net.sf.saxon.expr
Class TypeChecker

java.lang.Object
  extended bynet.sf.saxon.expr.TypeChecker

public class TypeChecker
extends java.lang.Object

This class provides Saxon's type checking capability. It contains a static method, staticTypeCheck, which is called at compile time to perform type checking of an expression. This class is never instantiated.


Constructor Summary
TypeChecker()
           
 
Method Summary
static Expression staticTypeCheck(Expression supplied, SequenceType req, boolean backwardsCompatible, RoleLocator role)
          Check an expression against a required type, modifying it if necessary.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

TypeChecker

public TypeChecker()
Method Detail

staticTypeCheck

public static Expression staticTypeCheck(Expression supplied,
                                         SequenceType req,
                                         boolean backwardsCompatible,
                                         RoleLocator role)
                                  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
backwardsCompatible - True if XPath 1.0 backwards compatibility mode is applicable
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)