spl_object_hash（）返回不同的id

Question

I'm learning about spl_object_hash() and don't quite understand what's behind the scene in this case:

$obj = new stdClass;
$id1 = spl_object_hash($obj);
$id2 = spl_object_hash(new stdClass);
echo $id1.'<br>'.$id2;

Q1. Why $id1 !== $id2?

In the reference:

When an object is destroyed, its hash may be reused for other objects.

Q.2 Is there something relates to that statement? Or I missed something else?

Answer 1

What does spl_object_hash do?

[Returns a] string that is unique for each currently existing object and is always the same for each object.

To clarify that statement: if you have object A, each time you hash object A, it'll return the same hash value. If you have object A and object B, even if both are of the same type and contain the same values, their hashes will differ, because they're not the same object (instance).

Since you have two different objects, it's expected that their respective ids differ.