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public interface FunctionLibrary
A FunctionLibrary handles the binding of function calls in XPath (or XQuery) expressions.
There are a number of implementations of this
class to handle different kinds of function: system functions, constructor functions, vendor-defined
functions, Java extension functions, stylesheet functions, and so on. There is also an implementation
FunctionLibraryList
that allows a FunctionLibrary
to be constructed by combining other FunctionLibrary objects.
Method Summary | |
---|---|
Expression |
bind(StructuredQName functionName,
Expression[] staticArgs,
StaticContext env,
Container container)
Bind a function, given the URI and local parts of the function name, and the list of expressions supplied as arguments. |
FunctionLibrary |
copy()
This method creates a copy of a FunctionLibrary: if the original FunctionLibrary allows new functions to be added, then additions to this copy will not affect the original, or vice versa. |
SequenceType[] |
getFunctionSignature(StructuredQName functionName,
int arity)
Test whether a function with a given name and arity is available; if so, return its signature. |
Method Detail |
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SequenceType[] getFunctionSignature(StructuredQName functionName, int arity)
This method may be called either at compile time or at run time. If the function library is to be used only in an XQuery or free-standing XPath environment, this method may throw an UnsupportedOperationException.
functionName
- the qualified name of the function being calledarity
- The number of arguments. This is set to -1 in the case of the single-argument
function-available() function; in this case the method should return a zero-lengh array
if there is some function of this name available for calling.
Expression bind(StructuredQName functionName, Expression[] staticArgs, StaticContext env, Container container) throws XPathException
functionName
- the QName of the function being calledstaticArgs
- The expressions supplied statically in arguments to the function call.
The length of this array represents the arity of the function. The intention is
that the static type of the arguments (obtainable via getItemType() and getCardinality()) may
be used as part of the binding algorithm. In some cases it may be possible for the function
to be pre-evaluated at compile time, for example if these expressions are all constant values.
The conventions of the XPath language demand that the results of a function depend only on the values of the expressions supplied as arguments, and not on the form of those expressions. For example, the result of f(4) is expected to be the same as f(2+2). The actual expression is supplied here to enable the binding mechanism to select the most efficient possible implementation (including compile-time pre-evaluation where appropriate).
env
- The static context of the function callcontainer
- The container for the newly created Expression
XPathException
- if a function is found with the required name and arity, but
the implementation of the function cannot be loaded or used; or if an error occurs
while searching for the function.FunctionLibrary copy()
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