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diff --git a/includes/MappedIterator.php b/includes/MappedIterator.php
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+<?php
+/**
+ * Convenience class for generating iterators from iterators.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ * @author Aaron Schulz
+ */
+
+/**
+ * Convenience class for generating iterators from iterators.
+ *
+ * @since 1.21
+ */
+class MappedIterator implements Iterator {
+	/** @var Iterator */
+	protected $baseIterator;
+	/** @var Closure */
+	protected $vCallback;
+
+	/**
+	 * Build an new iterator from a base iterator by having the former wrap the
+	 * later, returning the result of "value" callback for each current() invocation.
+	 * The callback takes the result of current() on the base iterator as an argument.
+	 * The keys of the base iterator are reused verbatim.
+	 *
+	 * @param Iterator|Array $iter
+	 * @param Closure $vCallback
+	 * @throws MWException
+	 */
+    public function __construct( $iter, Closure $vCallback ) {
+		if ( is_array( $iter ) ) {
+			$this->baseIterator = new ArrayIterator( $iter );
+		} elseif ( $iter instanceof Iterator ) {
+			$this->baseIterator = $iter;
+		} else {
+			throw new MWException( "Invalid base iterator provided." );
+		}
+		$this->vCallback = $vCallback;
+    }
+
+	/**
+	 * @return void
+	 */
+	public function rewind() {
+		$this->baseIterator->rewind();
+	}
+
+	/**
+	 * @return Mixed|null Returns null if out of range
+	 */
+	public function current() {
+		if ( !$this->baseIterator->valid() ) {
+			return null; // out of range
+		}
+		return call_user_func_array( $this->vCallback, array( $this->baseIterator->current() ) );
+	}
+
+	/**
+	 * @return Mixed|null Returns null if out of range
+	 */
+	public function key() {
+		if ( !$this->baseIterator->valid() ) {
+			return null; // out of range
+		}
+		return $this->baseIterator->key();
+	}
+
+	/**
+	 * @return void
+	 */
+	public function next() {
+		$this->baseIterator->next();
+	}
+
+	/**
+	 * @return bool
+	 */
+	public function valid() {
+		return $this->baseIterator->valid();
+	}
+}