gistfile1.php

<?php

$app['random_string'] = $app->protect(function (array $options = array()) {
	static $default_options = array(
		'length' => 5,
		'uppercase' => true,
		'lowercase' => true,
		'numeric' => true,
		'special_chars' => false,
		'chars' => 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789',
	);

	if (!empty($options))
	{
		$options = array_merge($default_options, $options);

		if ((bool) $options['uppercase'])
			$options['chars'] = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
		if ((bool) $options['lowercase'])
			$options['chars'] .= 'abcdefghijklmnopqrstuvwxyz';
		if ((bool) $options['numeric'])
			$options['chars'] .= '0123456789';
		if (!empty($options['special_chars']))
			$options['chars'] .= $options['special_chars'];

		if (!empty($options['remove_chars']))
			$options['chars'] = str_replace($options['remove_chars'], '', $options['chars']);

		if (isset($options['min_length']) && isset($options['max_length']))
			$options['length'] = (int) mt_rand($options['min_length'], $options['max_length']);

		$options['length'] = (int) $options['length'];
	}
	else
	{
		$options = $default_options;
	}

	$string = '';
	$char_len = strlen($options['chars']) - 1;

	for ($i = 0; $i < $options['length']; $i++)
		$string .= $options['chars'][mt_rand(0, $char_len)];

	return $string;
});
var_dump($this->app['random_string'](array('length' => 10)));

// error
// Fatal error: Function name must be a string in [the following line]
// var_dump($this->app['random_string'](array('length' => 10)));