Function that recursively changes the first character register of all keys in an array

arrayChangeFirstKeyCase.php

<?php

/**
 * Recursively changes the first character register of all keys in an array.
 * @param array $array The array to work on
 * @param int $case Either CASE_UPPER or CASE_LOWER (default)
 * @return array Returns an array with its keys lower or uppercase.
 *
 * Inspired by http://php.net/manual/en/function.array-change-key-case.php
 * @author Grigory Alexandrov <alexaandrov@gmail.com>
 */
function arrayChangeFirstKeyCase(array $array, $case = CASE_LOWER)
{
    switch ($case) {
        case CASE_LOWER:
            $callback = 'lcfirst';
            break;
        case CASE_UPPER:
            $callback = 'ucfirst';
            break;
        default:
            throw new \Exception('Incorrect case');
    }

    $formattedArray = [];
    foreach ($array as $key => $value) {
        $key = call_user_func($callback, $key);

        if (is_array($value)) {
            $value = arrayChangeFirstKeyCase($value, $case);
        }

        $formattedArray[$key] = $value;
    }

    return $formattedArray;
}