(PHP 5 >= 5.2.0, PHP 7)
spl_object_hash — Return hash id for given object
This function returns a unique identifier for the object. This id can be used as a hash key for storing objects, or for identifying an object, as long as the object is not destroyed. Once the object is destroyed, its hash may be reused for other objects.
A string that is unique for each currently existing object and is always the same for each object.
Example #1 A spl_object_hash() example
$id = spl_object_hash($object);
$storage[$id] = $object;
When an object is destroyed, its hash may be reused for other objects.