--- /dev/null
+<?php
+
+/**
+ * Extends ArrayObject and does two things:
+ *
+ * Allows for deriving classes to easily intercept additions
+ * and deletions for purposes such as additional indexing.
+ *
+ * Enforces the objects to be of a certain type, so this
+ * can be replied upon, much like if this had true support
+ * for generics, which sadly enough is not possible in PHP.
+ *
+ * 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
+ *
+ * @since 1.20
+ *
+ * @file
+ *
+ * @license GNU GPL v2+
+ * @author Jeroen De Dauw < jeroendedauw@gmail.com >
+ */
+abstract class GenericArrayObject extends ArrayObject {
+ /**
+ * Returns the name of an interface/class that the element should implement/extend.
+ *
+ * @since 1.20
+ *
+ * @return string
+ */
+ abstract public function getObjectType();
+
+ /**
+ * @see SiteList::getNewOffset()
+ * @since 1.20
+ * @var int
+ */
+ protected $indexOffset = 0;
+
+ /**
+ * Finds a new offset for when appending an element.
+ * The base class does this, so it would be better to integrate,
+ * but there does not appear to be any way to do this...
+ *
+ * @since 1.20
+ *
+ * @return int
+ */
+ protected function getNewOffset() {
+ while ( $this->offsetExists( $this->indexOffset ) ) {
+ $this->indexOffset++;
+ }
+
+ return $this->indexOffset;
+ }
+
+ /**
+ * @see ArrayObject::__construct
+ *
+ * @since 1.20
+ *
+ * @param null|array $input
+ * @param int $flags
+ * @param string $iterator_class
+ */
+ public function __construct( $input = null, $flags = 0, $iterator_class = 'ArrayIterator' ) {
+ parent::__construct( [], $flags, $iterator_class );
+
+ if ( !is_null( $input ) ) {
+ foreach ( $input as $offset => $value ) {
+ $this->offsetSet( $offset, $value );
+ }
+ }
+ }
+
+ /**
+ * @see ArrayObject::append
+ *
+ * @since 1.20
+ *
+ * @param mixed $value
+ */
+ public function append( $value ) {
+ $this->setElement( null, $value );
+ }
+
+ /**
+ * @see ArrayObject::offsetSet()
+ *
+ * @since 1.20
+ *
+ * @param mixed $index
+ * @param mixed $value
+ */
+ public function offsetSet( $index, $value ) {
+ $this->setElement( $index, $value );
+ }
+
+ /**
+ * Returns if the provided value has the same type as the elements
+ * that can be added to this ArrayObject.
+ *
+ * @since 1.20
+ *
+ * @param mixed $value
+ *
+ * @return bool
+ */
+ protected function hasValidType( $value ) {
+ $class = $this->getObjectType();
+ return $value instanceof $class;
+ }
+
+ /**
+ * Method that actually sets the element and holds
+ * all common code needed for set operations, including
+ * type checking and offset resolving.
+ *
+ * If you want to do additional indexing or have code that
+ * otherwise needs to be executed whenever an element is added,
+ * you can overload @see preSetElement.
+ *
+ * @since 1.20
+ *
+ * @param mixed $index
+ * @param mixed $value
+ *
+ * @throws InvalidArgumentException
+ */
+ protected function setElement( $index, $value ) {
+ if ( !$this->hasValidType( $value ) ) {
+ throw new InvalidArgumentException(
+ 'Can only add ' . $this->getObjectType() . ' implementing objects to '
+ . static::class . '.'
+ );
+ }
+
+ if ( is_null( $index ) ) {
+ $index = $this->getNewOffset();
+ }
+
+ if ( $this->preSetElement( $index, $value ) ) {
+ parent::offsetSet( $index, $value );
+ }
+ }
+
+ /**
+ * Gets called before a new element is added to the ArrayObject.
+ *
+ * At this point the index is always set (ie not null) and the
+ * value is always of the type returned by @see getObjectType.
+ *
+ * Should return a boolean. When false is returned the element
+ * does not get added to the ArrayObject.
+ *
+ * @since 1.20
+ *
+ * @param int|string $index
+ * @param mixed $value
+ *
+ * @return bool
+ */
+ protected function preSetElement( $index, $value ) {
+ return true;
+ }
+
+ /**
+ * @see Serializable::serialize
+ *
+ * @since 1.20
+ *
+ * @return string
+ */
+ public function serialize() {
+ return serialize( $this->getSerializationData() );
+ }
+
+ /**
+ * Returns an array holding all the data that should go into serialization calls.
+ * This is intended to allow overloading without having to reimplement the
+ * behavior of this base class.
+ *
+ * @since 1.20
+ *
+ * @return array
+ */
+ protected function getSerializationData() {
+ return [
+ 'data' => $this->getArrayCopy(),
+ 'index' => $this->indexOffset,
+ ];
+ }
+
+ /**
+ * @see Serializable::unserialize
+ *
+ * @since 1.20
+ *
+ * @param string $serialization
+ *
+ * @return array
+ */
+ public function unserialize( $serialization ) {
+ $serializationData = unserialize( $serialization );
+
+ foreach ( $serializationData['data'] as $offset => $value ) {
+ // Just set the element, bypassing checks and offset resolving,
+ // as these elements have already gone through this.
+ parent::offsetSet( $offset, $value );
+ }
+
+ $this->indexOffset = $serializationData['index'];
+
+ return $serializationData;
+ }
+
+ /**
+ * Returns if the ArrayObject has no elements.
+ *
+ * @since 1.20
+ *
+ * @return bool
+ */
+ public function isEmpty() {
+ return $this->count() === 0;
+ }
+}
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