Multiple response sets

InfoRecordSet.php

<?php

class InfoRecordSet extends \ArrayObject
{
    public function getIterator()
    {
        $this->ksort();
        return parent::getIterator();
    }


}

MultipleResponseSets.php

<?php

class MultipleResponseSets extends Info
{
    public const SUBTYPE = 19;
    public const TYPE_CATEGORIES = 'C';
    public const TYPE_DICHOTOMIES_VAR_LABELS = 'D';
    public const TYPE_DICHOTOMIES_COUNTED_LABELS = 'E';

    /**
     * @param string $name
     * @param string $type
     * @param Variable[] $variables
     * @param string|null $label
     */
    public function addSet(
        string $name,
        string $type,
        array $variables,
        ?string $label = null
    ) {
        $this->data[] = [
            'name' => $name,
            'type' => $type,
            'label' => $label,
            'variables' => $variables
        ];


    }

    public function write(Buffer $buffer)
    {
        $data = '';
        foreach($this->data as [
            'name' => $name,
            'type' => $type,
            'label' => $label,
            'variables' => $variables
        ]) {
            $countedValue = 1;
            $countedValueLength = strlen($countedValue);
            $labelLength = $label ? strlen($label) : 0;
            $data .= '$' . $name . "={$type} 1 $countedValueLength $countedValue $labelLength $label";
            foreach($variables as $variable) {
                $data .= ' ' . $variable->name;
            }
            $data .= "\n";
        }
        $this->dataCount = strlen($data);
        parent::write($buffer);
        $buffer->write($data);
    }
}

usage.php

<?php

$writer = new Writer();
// Since the writer puts data into the info record set, but SPSS file format spec requires info records to be ordered I implemented a class that enforces ordered iteration.
$writer->info = new InfoRecordSet();