What is null coalescing assignment ??= operator in PHP 7.4

Question

I\'ve just seen a video about upcoming PHP 7.4 features and saw this new ??= operator. I already know the ?? operator.

How\'s this different

Answer 1

Example Docs:

$array['key'] ??= computeDefault();
// is roughly equivalent to
if (!isset($array['key'])) {
    $array['key'] = computeDefault();
}