<?php

// input data
$a = 'first';
$b = 'second';
$array = [&$a, &$b];

/**
 * Do something with array an return of modified array
 * @param string[] $input
 * @return array
 */
function doSomething(array $input) {
	$result = $input;
	foreach ($result as &$val) {
		$val = str_rot13($val);
	}
	
	return $result;
}

printf('$a=%s $b=%s' . PHP_EOL, $a, $b);
doSomething($array);
printf('$a=%s $b=%s' . PHP_EOL, $a, $b);