I agree that some people might want a mb_explode('', $string);

this is my solution for it:

<?php

$string = 'Hallöle';

$array = array_map(function ($i) use ($string) { 
    return mb_substr($string, $i, 1); 
}, range(0, mb_strlen($string) -1));

expect($array)->toEqual(['H', 'a', 'l', 'l', 'ö', 'l', 'e']);

?>