Although my implementation using array_udiff() was bad (it only works for a subset of cases), using array_udiff() to filter elements is a bad idea anyway because of the underlying sorting algorithms applied to the arrays.

Nevertheless, I like the RFC's idea, highlighted by @mickmackusa, of being able to use certain array operations on enumeration arrays.

The implementation below using array_udiff() with the spaceship operator and the enumeration name works now correctly, but is nevertheless very slow with large arrays.

array_udiff($all, $filtered, fn($item1, $item2) => $item1->name <=> $item2->name) ;

I performed performance tests with the following functions using a hundred-value enumeration class:

• foreach and in_array()
• array_reduce() and in_array()
• array_filter() and in_array()
• array_walk() and in_array()
• array_udiff()

On my hardware with PHP 8.4, using the foreach loop in conjunction with the in_array() function gives the fastest results, while using the array_reduce() and array_filter() functions instead is about ~20% slower, the array_walk() function is about ~30% slower, and using the array_udiff() function is by far much slower, by over 380%.

array_reduce($all, function ($carry, $case) use ($filtered) {
    if (!in_array($case, $filtered, true)) {
        $carry[] = $case;
    }
    return $carry;
}, []);

array_filter($all, fn($case) => !in_array($case, $filtered, true));

$diff = [];
array_walk($all, function ($value) use ($filtered, &$diff) {
    if (!in_array($value, $filtered, true)) {
        $diff[] = $value;
    }
}, $diff);