Bug->Doc #70418 [Ver]: SplObjectStorage not replacing objects when hash matches

Edit report at https://bugs.php.net/bug.php?id=70418&edit=1

 ID:                 70418
 Updated by:         [email protected]
 Reported by:        richardh at channelgrabber dot com
 Summary:            SplObjectStorage not replacing objects when hash
                     matches
 Status:             Verified
-Type:               Bug
+Type:               Documentation Problem
 Package:            SPL related
 PHP Version:        5.5.28
 Block user comment: N
 Private report:     N

 New Comment:

> Of course, that works fine with the default hashes...

And given that it behaves like that since "forever", I suggest to
document that ::getHash()[1] is supposed to return unique hashes,
and to clarify

| The storage object will never contain more than one object with
| the same identifier.

in case of hash collissions.

[1] <https://www.php.net/manual/en/splobjectstorage.gethash.php>


Previous Comments:
------------------------------------------------------------------------
[2015-09-03 17:22:20] [email protected]

Actually, that behavior[1] is part of the ability to store
additional info with the object. The idea is obviously that it
should be possible to change the info only, but leave the object
as is, by calling ::attach() again with the same object. Of
course, that works fine with the default hashes...

[1] <https://github.com/php/php-src/blob/php-5.6.12/ext/spl/spl_observer.c#L220-L225>

------------------------------------------------------------------------
[2015-09-03 15:11:15] [email protected]

Confirmed: <https://3v4l.org/i1v7q>

------------------------------------------------------------------------
[2015-09-03 11:32:31] richardh at channelgrabber dot com

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:
---------------
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"


------------------------------------------------------------------------



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Edit this bug report at https://bugs.php.net/bug.php?id=70418&edit=1