Description:
------------
If you change how the SplObjectStorage calculates an objects hash, and then attach an object which will create the same hash as a currently stored object, SplObjectStorage will silently drop the new object rather than replacing the current object at that hash with the new one. This means that if the object differs from the stored object, those changes are also dropped which can result in unexpected behaviour when iterating over the stored objects.

This conflict with how arrays work when reassigning a value for the same index.

Test script:
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class IdObjectStorage extends SplObjectStorage {
    public function getHash($object) { return (string) $object->id; }
}

$storage = new IdObjectStorage(); $array = [];

$object1 = new stdClass(); $object1->id = 1; $object1->value = 'Object #1';
$storage->attach($object1);
$array[$object1->id] = $object1;

foreach($storage as $x) var_dump($x->value); // Object #1
foreach($array as $x)   var_dump($x->value); // Object #1

$object2 = new stdClass(); $object2->id = 1; $object2->value = 'Object #2';
$array[$object2->id] = $object2;
$storage->attach($object2);

foreach($storage as $x) var_dump($x->value); // Object #1
foreach($array as $x)   var_dump($x->value); // Object #2

Expected result:
----------------
SplObjectStorage should work the same as arrays, in that when an object is attached with the same hash as a current entry, that entry is replaced with the new object.

string(9) "Object #1"
string(9) "Object #1"
string(9) "Object #2"
string(9) "Object #2"

Actual result:
--------------
SplObjectStorage silently drops the new object as it already has an object for that hash.

string(9) "Object #1"
string(9) "Object #1"
string(9) "Object #1"
string(9) "Object #2"