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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2013 Saxonica Limited.
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.expr;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.trans.XPathException;
/**
* MappingIterator merges a sequence of sequences into a single flat
* sequence. It takes as inputs an iteration, and a mapping function to be
* applied to each Item returned by that iteration. The mapping function itself
* returns another iteration. The result is an iteration of the concatenation of all
* the iterations returned by the mapping function.
*
* This is a powerful class. It is used, with different mapping functions,
* in a great variety of ways. It underpins the way that "for" expressions and
* path expressions are evaluated, as well as sequence expressions. It is also
* used in the implementation of the document(), key(), and id() functions.
*/
public class MappingIterator
implements SequenceIterator {
private SequenceIterator base;
private MappingFunction action;
/*@Nullable*/ private SequenceIterator results = null;
//private boolean atomizing = false;
private T current = null;
private int position = 0;
/**
* Construct a MappingIterator that will apply a specified MappingFunction to
* each Item returned by the base iterator.
* @param base the base iterator
* @param action the mapping function to be applied
*/
public MappingIterator(SequenceIterator base, MappingFunction action) {
this.base = base;
this.action = action;
}
public T next() throws XPathException {
T nextItem;
while (true) {
if (results != null) {
nextItem = results.next();
if (nextItem != null) {
break;
} else {
results = null;
}
}
F nextSource = base.next();
if (nextSource != null) {
// Call the supplied mapping function
SequenceIterator obj = action.map(nextSource);
// The result may be null (representing an empty sequence),
// or a SequenceIterator (any sequence)
if (obj != null) {
results = obj;
nextItem = results.next();
if (nextItem == null) {
results = null;
} else {
break;
}
}
// now go round the loop to get the next item from the base sequence
} else {
results = null;
current = null;
position = -1;
return null;
}
}
current = nextItem;
position++;
return nextItem;
}
public T current() {
return current;
}
public int position() {
return position;
}
public void close() {
if (results != null) {
results.close();
}
base.close();
}
/*@NotNull*/
public SequenceIterator getAnother() throws XPathException {
SequenceIterator newBase = base.getAnother();
MappingFunction newAction = action instanceof StatefulMappingFunction ?
(MappingFunction)((StatefulMappingFunction)action).getAnother() :
action;
return new MappingIterator(newBase, newAction);
}
/**
* Get properties of this iterator, as a bit-significant integer.
*
* @return the properties of this iterator. This will be some combination of
* properties such as {@link SequenceIterator#GROUNDED}, {@link SequenceIterator#LAST_POSITION_FINDER},
* and {@link SequenceIterator#LOOKAHEAD}. It is always
* acceptable to return the value zero, indicating that there are no known special properties.
* It is acceptable for the properties of the iterator to change depending on its state.
*/
public int getProperties() {
return 0;
}
}