package net.sf.saxon.functions;
import net.sf.saxon.expr.*;
import net.sf.saxon.om.*;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.Cardinality;
import net.sf.saxon.value.EmptySequence;
import net.sf.saxon.value.NumericValue;
import net.sf.saxon.value.SequenceType;
/**
* Implements the saxon:item-at() function. This is handled specially because it is generated
* by the optimizer.
*
* <p>The function takes two arguments: the first is an arbitrary sequence, the second is optional numeric.
* The function returns the same result as let $N := NUMBER return SEQUENCE[$N], including cases where the
* numeric argument is not a whole number.</p>
*/
public class ItemAt extends ExtensionFunctionDefinition {
private static final StructuredQName qName =
new StructuredQName("", NamespaceConstant.SAXON, "item-at");
/**
* Get the function name, as a QName
* @return the QName of the function
*/
public StructuredQName getFunctionQName() {
return qName;
}
/**
* Get the minimum number of arguments required by the function
* @return the minimum number of arguments that must be supplied in a call to this function
*/
public int getMinimumNumberOfArguments() {
return 2;
}
/**
* Get the maximum number of arguments allowed by the function
* @return the maximum number of arguments that may be supplied in a call to this function
*/
public int getMaximumNumberOfArguments() {
return 2;
}
/**
* Get the required types for the arguments of this function, counting from zero
* @return the required types of the argument, as defined by the function signature. Normally
* this should be an array of size {@link #getMaximumNumberOfArguments()}; however for functions
* that allow a variable number of arguments, the array can be smaller than this, with the last
* entry in the array providing the required type for all the remaining arguments.
*/
public SequenceType[] getArgumentTypes() {
return argumentTypes;
}
private static SequenceType[] argumentTypes = new SequenceType[] {
SequenceType.ANY_SEQUENCE,
SequenceType.OPTIONAL_NUMERIC
};
/**
* Get the type of the result of the function
* @param suppliedArgumentTypes the static types of the arguments to the function.
* This is provided so that a more precise result type can be returned in the common
* case where the type of the result depends on the type of the first argument. The value
* will be null if the function call has no arguments.
* @return the return type of the function, as defined by its function signature
*/
public SequenceType getResultType(SequenceType[] suppliedArgumentTypes) {
return SequenceType.makeSequenceType(
suppliedArgumentTypes[0].getPrimaryType(), StaticProperty.ALLOWS_ZERO_OR_ONE);
}
/**
* Create a call on this function. This method is called by the compiler when it identifies
* a function call that calls this function.
*/
public ExtensionFunctionCall makeCallExpression() {
return new ItemAtCall();
}
/**
* Return an object capable of compiling this IntegratedFunction call to Java source code. The returned
* object may be null, in which case Java code generation is not supported for this IntegratedFunction.
* If the returned object is not null, it must implement the interface
* com.saxonica.codegen.IntegratedFunctionCompiler. The default implementation returns null
* @return an instance of com.saxonica.codegen.IntegratedFunctionCompiler that generates Java code
* to implement the call on this extension function
*/
public Object getCompilerForJava() {
try {
return Class.forName("com.saxonica.codegen.ItemAtCompiler").newInstance();
} catch (InstantiationException e) {
return null;
} catch (IllegalAccessException e) {
return null;
} catch (ClassNotFoundException e) {
return null;
}
}
private static class ItemAtCall extends ExtensionFunctionCall {
/**
* Optimize the function call. This method is called at compile time if expression optimization
* is enabled. It gives the implementation an opportunity to replace itself with an optimized implementation
* that returns the same result.
* @param context The static context in which the function call appears. The method must not modify
* the static context.
* @param arguments 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.
* @return an expression to be evaluated at run-time in place of this function call. Return null
* if no optimization is possible and the function call should be used unchanged. Return a
* {@link net.sf.saxon.expr.Literal} representing the result of the function call if the function call
* can be precomputed at compile time
* @throws net.sf.saxon.trans.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 {
if (arguments[1] instanceof Literal) {
NumericValue val = (NumericValue)((Literal)arguments[1]).getValue();
if (val.compareTo(1) < 0 || val.compareTo(Integer.MAX_VALUE) > 0 || !val.isWholeNumber()) {
return new Literal(EmptySequence.getInstance());
}
if (val.compareTo(1) > 0 && !Cardinality.allowsMany(arguments[0].getCardinality())) {
return new Literal(EmptySequence.getInstance());
}
}
return null;
}
/**
* Evaluate this function call at run-time
* @param 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. If required, the
* supplied sequence can be materialized by calling, for example, <code>new SequenceExtent(arguments[i])</code>.
* If the argument is always a singleton, then the single item may be obtained by calling
* <code>arguments[i].next()</code>. The implementation is not obliged to read all the items in each
* <code>SequenceIterator</code> 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.
* @param context The XPath dynamic evaluation context
* @return an iterator over the results of the function. If the result is a single item, it can be
* returned in the form of a {@link net.sf.saxon.om.SingletonIterator}. If the result is an empty sequence,
* the method should return <code>EmptyIterator.getInstance()</code>
* @throws net.sf.saxon.trans.XPathException
* if a dynamic error occurs during evaluation of the function. The Saxon run-time
* code will add information about the error location.
*/
public SequenceIterator call(SequenceIterator[] arguments, XPathContext context) throws XPathException {
NumericValue index = (NumericValue)arguments[1].next();
if (index == null) {
return EmptyIterator.getInstance();
}
if (index.compareTo(Integer.MAX_VALUE) <= 0 && index.isWholeNumber()) {
int intindex = (int)index.longValue();
if (intindex < 1) {
return EmptyIterator.getInstance();
}
Item item;
SequenceIterator base = arguments[0];
if (intindex == 1) {
item = base.next();
} else if (base instanceof GroundedIterator) {
GroundedValue value = ((GroundedIterator)base).materialize();
item = value.itemAt(intindex-1);
} else {
SequenceIterator tail = TailIterator.make(base, intindex);
item = tail.next();
}
return SingletonIterator.makeIterator(item);
} else {
// there is no item at the required position
return EmptyIterator.getInstance();
}
}
}
}
//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
// you may not use this file except in compliance with the License. You may obtain a copy of the
// License at http://www.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Contributor(s):
//