net.sf.saxon.expr
Class TypeChecker

java.lang.Object
  net.sf.saxon.expr.TypeChecker

public final class TypeChecker
extends 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.

Method Summary

static XPathException	ebvError(Expression exp, TypeHierarchy th) Test whether a given expression is capable of returning a value that has an effective boolean value.
static Expression	staticTypeCheck(Expression supplied, SequenceType req, boolean backwardsCompatible, RoleLocator role, ExpressionVisitor visitor) Check an expression against a required type, modifying it if necessary.
static Expression	strictTypeCheck(Expression supplied, SequenceType req, RoleLocator role, StaticContext env) Check an expression against a required type, modifying it if necessary.
static XPathException	testConformance(ValueRepresentation val, SequenceType requiredType, XPathContext context) Test whether a given value conforms to a given type

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

staticTypeCheck

public static Expression staticTypeCheck(Expression supplied,
                                         SequenceType req,
                                         boolean backwardsCompatible,
                                         RoleLocator role,
                                         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

backwardsCompatible - True if XPath 1.0 backwards compatibility mode is applicable

role - 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)

strictTypeCheck

public static Expression strictTypeCheck(Expression supplied,
                                         SequenceType req,
                                         RoleLocator role,
                                         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, boolean, net.sf.saxon.expr.RoleLocator, net.sf.saxon.expr.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

role - 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(ValueRepresentation 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