Variable.php

<?php
/*
 * citeproc-php
 *
 * @link        http://github.com/seboettg/citeproc-php for the source repository
 * @copyright   Copyright (c) 2016 Sebastian Böttger.
 * @license     https://opensource.org/licenses/MIT
 */
 
namespace Seboettg\CiteProc\Constraint;
 
use stdClass;
 
class Variable extends AbstractConstraint
{
    protected function matchForVariable($variable, $data)
    {
        return !empty($data->{$variable});
    }
}