<?php

function explode_list(string $str) : array {
    if (($str = trim($str, " \n\r\t\v\0,")) !== "") {
        return array_map(fn($a) => trim($a), explode(",", str_replace(" ", "", $str)));
    } else {
        return [];
    }
}

function alter_array_contents(array &$a, $add, $remove) {
    if (($add !== null) && !array_search($add, $a)) { // if user was not assigned to the corresponding group
        $a[] = $add;
    }
    if (($remove !== null) && (($i = array_search($remove, $a)) !== false)) { // only perform deleting if user is assigned to the passed group
        array_splice($a, $i, 1);
    }
}