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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 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;
import net.sf.saxon.transpile.CSharpDelegate;

/**
 * MappingFunction is an interface that must be satisfied by an object passed to a
 * MappingIterator. It represents an object which, given an Item, can return a
 * SequenceIterator that delivers a sequence of zero or more Items.
 *
 * It maps an item of class F to a sequence of items of class T, returned as an iterator.
 *
 *  NOTE: Java allows a lambda expression to be used where an ItemMappingFunction
 *  is needed, but C# does not (it's not possible in C# to have a class implementing
 *  a delegate). So if a delegate is wanted, use {@link SequenceMapper}.
 */

@FunctionalInterface
@CSharpDelegate(false)
public interface MappingFunction {

    /**
     * Map one item to a sequence.
     *
     * @param item The item to be mapped.
     * @return one of the following: (a) a SequenceIterator over the sequence of items that the supplied input
     *         item maps to, or (b) null if it maps to an empty sequence.
     * @throws XPathException if a dynamic error occurs
     */

    /*@Nullable*/
    SequenceIterator map(Item item) throws XPathException;

}