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java.lang.Object net.sf.saxon.lib.ExtensionFunctionCall
public abstract class ExtensionFunctionCall
This abstract class is provided to allow user-written extension functions to be implemented with the full capabilities of functions that are an intrinsic part of the Saxon product. In particular, the class has the opportunity to save data from the static context and to optimize itself at compile time.
Instances of this class are created by calling the method makeCallExpression() on the
ExtensionFunctionDefinition
object that represents the definition of the function.
The compiler will create one instance of this class for each function call appearing in the expression being compiled. The class must therefore have a public zero-argument constructor.
The compiler will ensure that the supplied arguments in the extension function call are converted if necessary to the declared argument types, by applying the standard conversion rules. The result returned by the function is checked against the declared return type, but no conversion takes place: the returned value must strictly conform to the declared type.
Note that an IntegratedFunction is trusted; calls are allowed even if the configuration option
FeatureKeys.ALLOW_EXTERNAL_FUNCTIONS
is false. In cases where an IntegratedFunction
is used to load and execute untrusted code, it should check this configuration option before doing so.
Constructor Summary | |
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ExtensionFunctionCall()
|
Method Summary | |
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abstract SequenceIterator<? extends Item> |
call(SequenceIterator<? extends Item>[] arguments,
XPathContext context)
Evaluate this function call at run-time |
void |
copyLocalData(ExtensionFunctionCall destination)
Copy local data from one copy of the function to another. |
boolean |
effectiveBooleanValue(SequenceIterator<? extends Item>[] arguments,
XPathContext context)
Compute the effective boolean value of the result. |
Container |
getContainer()
Get the container of the expression. |
ExtensionFunctionDefinition |
getDefinition()
Get the definition of this extension function |
Executable |
getExecutable()
Get the Executable in which this extension function call occurs |
Expression |
rewrite(StaticContext context,
Expression[] arguments)
Rewrite the function call. |
void |
setDefinition(ExtensionFunctionDefinition definition,
Container container)
This method is called by the system to provide information about the extension function call. |
void |
supplyStaticContext(StaticContext context,
int locationId,
Expression[] arguments)
Supply static context information. |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
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public ExtensionFunctionCall()
Method Detail |
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public final void setDefinition(ExtensionFunctionDefinition definition, Container container)
definition
- the extension function definitioncontainer
- the container of the extension function call, providing access to location informationpublic final ExtensionFunctionDefinition getDefinition()
public final Executable getExecutable()
public final Container getContainer()
public void supplyStaticContext(StaticContext context, int locationId, Expression[] arguments) throws XPathException
This method is called during compilation to provide information about the static context in which the function call appears. If the implementation of the function needs information from the static context, then it should save it now, as it will not be available later at run-time.
The implementation also has the opportunity to examine the expressions that appear in the arguments to the function call at this stage. These might already have been modified from the original expressions as written by the user. The implementation must not modify any of these expressions.
The default implementation of this method does nothing.
context
- The static context in which the function call appears. The method must not modify
the static context.locationId
- An integer code representing the location of the call to the extension function
in the stylesheet; can be used in conjunction with the locationMap held in the static context for diagnosticsarguments
- The XPath expressions supplied in the call to this function. The method must not
modify this array, or any of the expressions contained in the array.
XPathException
- if the implementation is able to detect a static error in the way the
function is being called (for example it might require that the types of the arguments are
consistent with each other).public Expression rewrite(StaticContext context, Expression[] arguments) throws XPathException
There is also a further opportunity to perform static checking at this stage and to throw an error if the arguments are invalid.
context
- The static context in which the function call appears. The method must not modify
the static context.arguments
- The XPath expressions supplied in the call to this function. This method is called
after type-checking, so these expressions may have been modified by adding atomization operators
or type-checking operations, for example.
Literal
representing the result of the function call if the function call
can be precomputed at compile time
XPathException
- if the implementation is able to detect a static error in the way the
function is being called (for example it might require that the types of the arguments are
consistent with each other).public void copyLocalData(ExtensionFunctionCall destination)
This method is called if a call to the extension function needs to be copied during the process of optimization. For example, this occurs if the function containing the call to the extension function is inlined.
If any objects held as local data for the function call are mutable then deep copies must be made.
destination
- the function to which the local data must be copied. This will always
be an instance of the same function class as the source function.public abstract SequenceIterator<? extends Item> call(SequenceIterator<? extends Item>[] arguments, XPathContext context) throws XPathException
arguments
- The values of the arguments to the function call. Each argument value (which is in general
a sequence) is supplied in the form of an iterator over the items in the sequence. Any required conversions
to the declared types of the arguments will already have been performed.
If required, the supplied sequence can be materialized by calling, for example,
new SequenceExtent(arguments[i])
.
If the argument is always a singleton, then the single item may be obtained by calling
arguments[i].next()
.
The implementation is not obliged to read all the items in each SequenceIterator
if they are not required to compute the result; but if any SequenceIterator
is not read
to completion, it is good practice to call its close()
method.
context
- The XPath dynamic evaluation context
The implementation is responsible for ensuring that the result is a valid instance of the declared
result type. Saxon will check that this is the case if the ExtensionFunctionDefinition.trustResultType()
method returns false, but it will never convert the supplied result value to the declared result type.
If the result is a single item, it can be returned in the form of a SingletonIterator
.
If the result is an empty sequence, the method should return EmptyIterator.getInstance()
XPathException
- if a dynamic error occurs during evaluation of the function. The Saxon run-time
code will add information about the error location.public boolean effectiveBooleanValue(SequenceIterator<? extends Item>[] arguments, XPathContext context) throws XPathException
Implementations can override this method but are not required to do so. If it is overridden, the result must be consistent with the rules for calculating effective boolean value. The method should be implemented in cases where computing the effective boolean value is significantly cheaper than computing the full result.
context
- The XPath dynamic evaluation contextarguments
- The values of the arguments to the function call. Each argument value (which is in general
a sequence) is supplied in the form of an iterator over the items in the sequence. If required, the
supplied sequence can be materialized by calling, for example, new SequenceExtent(arguments[i])
.
If the argument is always a singleton, then the single item may be obtained by calling
arguments[i].next()
. The implementation is not obliged to read all the items in each
SequenceIterator
if they are not required to compute the result; but if any SequenceIterator is not read
to completion, it is good practice to call its close() method.
XPathException
- if a dynamic error occurs during evaluation of the function. The Saxon run-time
code will add information about the error location.
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