GenericArrayObject.php

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<?php

abstract class GenericArrayObject extends ArrayObject {

        abstract public function getObjectType();

        protected $indexOffset = 0;

        protected function getNewOffset() {
                while ( $this->offsetExists( $this->indexOffset ) ) {
                        $this->indexOffset++;
                }

                return $this->indexOffset;
        }

        public function __construct( $input = null, $flags = 0, $iterator_class = 'ArrayIterator' ) {
                parent::__construct( array(), $flags, $iterator_class );

                if ( !is_null( $input ) ) {
                        foreach ( $input as $offset => $value ) {
                                $this->offsetSet( $offset, $value );
                        }
                }
        }

        public function append( $value ) {
                $this->setElement( null, $value );
        }

        public function offsetSet( $index, $value ) {
                $this->setElement( $index, $value );
        }

        protected function hasValidType( $value ) {
                $class = $this->getObjectType();
                return $value instanceof $class;
        }

        protected function setElement( $index, $value ) {
                if ( !$this->hasValidType( $value ) ) {
                        throw new InvalidArgumentException(
                                'Can only add ' . $this->getObjectType() . ' implementing objects to ' . get_called_class() . '.'
                        );
                }

                if ( is_null( $index ) ) {
                        $index = $this->getNewOffset();
                }

                if ( $this->preSetElement( $index, $value ) ) {
                        parent::offsetSet( $index, $value );
                }
        }

        protected function preSetElement( $index, $value ) {
                return true;
        }

        public function serialize() {
                return serialize( $this->getSerializationData() );
        }

        protected function getSerializationData() {
                return array(
                        'data' => $this->getArrayCopy(),
                        'index' => $this->indexOffset,
                );
        }

        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;
        }

        public function isEmpty() {
                return $this->count() === 0;
        }

}