Re: In php 8.0: unable to distinguish between instance variable being null and unset

Some values can be null! So that's why isset won't work.

On Sun, 5 Sep 2021 at 15:33, Alexandru Pătrănescu <[email protected]>
wrote:

> Hey Emiel,
>
> On Sun, Sep 5, 2021 at 3:13 PM Emiel Mols <[email protected]> wrote:
>
>> Thanks for the detailed answer Alexandru. Indeed our use case is an
>> ActiveRecord pattern where we lazily deserialize complex (json) variables
>> only when accessed. This is a performance as we have quite wide objects and
>> deserialization is quite expensive (100s of fields, and only need a few);
>> simplified/pseudo:
>>
>> abstract class Record {
>> public function hydrate(array $data) {
>>     $this->rawData = $data;
>>     foreach (static::keys() as $key) { unset($this->{$key}); } // unset
>> indicates they need to be populated from rawData later
>> }
>> public function __get(string $key) {
>>    $this->{$key} = static::deserialize($key); // can be expensive-ish
>>    return $this->{$key};
>> }
>> public function changedValues(): array {
>>    $changed = [];
>>    foreach (static::keys() as $key) {
>>        // magical isUnset we don't have right now - should return false
>> when null
>>        if (!isUnset($this->{$key}}) {
>>            $changed[$key] = $this->{$key};
>>        }
>>    }
>>    return $changed;
>> }
>> }
>>
>
> Thanks for providing the sample code.
>
> If you change the method to something like this, I'm pretty sure it's
> going to be similarly fast on PHP 7.4, possibly even faster:
>
> public function changedValues(): array {
>     $changed = [];
>     $values = (array)$this;
>     foreach (static::keys() as $key) {
>         if (isset($values[$key])) {
>             $changed[$key] = $values[$key];
>         }
>     }
>     return $changed;
> }
>
>
> Just give it a try!
>
> Regards,
> Alex
>
>
>> After your suggestion that array_key_exists($k, (array)$object) has the
>> same behavior, I had a look into the pre-8.0 code <
>> https://github.com/php/php-src/commit/c46b2ed677aecfc2f07993eefad0326f31c5cc44>.
>> Indeed it seems to do exactly the same (namely convert to array first, then
>> do the operation), but that means in our case the operation is
>> unnecessarily expensive (also on 7.4): we're converting to those arrays
>> (with 100s of elements) all the time. And we would be a lot better off if
>> we have a cheaper check to see if a field is actually set on an object
>> instance (ignoring whether it is defined).
>>
>> In terms of a suggestion to extend an existing function to support this:
>> property_exist($object, $key, $ignoreDefined=false). When the
>> $ignoreDefined, the path that checks definition on the class could be
>> skipped <
>> https://github.com/php/php-src/blob/a13730c5e465b3c349a7970d15a49e4e132d4e07/Zend/zend_builtin_functions.c#L943>.
>> Not sure about the comprehensibility of such a flag, though.
>>
>> Thanks!
>>
>>
>> On Sun, Sep 5, 2021 at 5:51 AM Alexandru Pătrănescu <[email protected]>
>> wrote:
>>
>>>
>>> On Sat, Sep 4, 2021 at 11:26 PM Alexandru Pătrănescu <[email protected]>
>>> wrote:
>>>
>>>> Hey Emiel,
>>>>
>>>>
>>>> On Fri, Sep 3, 2021 at 3:09 PM Emiel Mols <[email protected]> wrote:
>>>>
>>>>> Hello,
>>>>>
>>>>> Our codebase depends on distinguishing whether an instance variable is
>>>>> unset, or simply null:
>>>>>
>>>>
>>>> Can you please share more on how you use this information? Is it for
>>>> lazy loading something that might not be loadable in the end?
>>>>
>>>>
>>>>>
>>>>> class C { public int $v = 123; }
>>>>> $x = new C; unset($x->v);
>>>>> $y = new C; $u->v = null;
>>>>>
>>>>> In php <8.0 we made this work with @array_key_exists($x, 'v'), which
>>>>> stopped working. isset($x->x) doesn't work, as it will return true for
>>>>> 'null' as well. property_exists($x, 'v') will always return true as long as
>>>>> the variable is declared: php-src here
>>>>> <https://github.com/php/php-src/blob/a13730c5e465b3c349a7970d15a49e4e132d4e07/Zend/zend_builtin_functions.c#L943>
>>>>> .
>>>>>
>>>>> Apart from using debug_zval_dump (too expensive), any hints?
>>>>>
>>>>
>>>> I think the simplest solution would be to cast the object to an array
>>>> and you will see that the unset property will not be a key in the array
>>>> while the null one will be.
>>>>
>>>
>>> Just to have it clear for anyone that might be following the
>>> thread later:
>>> Basically *array_key_exists('propName', $object);* until 8.0
>>> Is equivalent with *array_key_exists('propName', (array)$object);*
>>> starting with 8.0
>>> Of course, this fix should be applied starting with PHP 7.4 to remove
>>> the deprecation warning, not hide it with the silent operator.
>>> You can check how it works based on your last example:
>>> https://3v4l.org/7L3qP
>>>
>>>
>>>> Another way to go here would be to use the magic method __get() that
>>>> would be called on the unset property. But not sure how that fits with your
>>>> use case.
>>>> Also something like this could work: https://3v4l.org/7NL0Y, trying to
>>>> read the property and handling the Error thrown.
>>>> But it all depends on how you use this... Please share more to help you
>>>> correctly.
>>>>
>>>>
>>>>> This feels like quite the oversight honestly :).
>>>>>
>>>>
>>>> This feels like quite a special use case that could be implemented
>>>> differently to start with. Please share more information so we can help
>>>> better.
>>>> I guess you have read the rfc that deprecated this in 7.4 and scheduled
>>>> for later removal:
>>>> https://wiki.php.net/rfc/deprecations_php_7_4#array_key_exists_with_objects
>>>>
>>>>
>>>>>
>>>>> Best,
>>>>>
>>>>> Emiel
>>>>>
>>>>
>>>> Alex
>>>>
>>>