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php

unsetting class properties

php.internals

(Marcus Börger)

23 years ago

Hello Zeev, hi Andi,

atm it is not possible to unset static members of a class which is correct
since that would modify the class protocol. But it is possible to unset non
dynamic properties (defined in the class). This should also be prevented as
done with the attached patch.

I did it by checking whether the name is part of the default properties. This
works but maybe it is to slow. So perhaps it is a better solution to provide a
flag in the property_info but then we#d have to do that in every class
instantiation while my method would only take time when unset is used on
props.

Test code:
<?php
class u { var $x = 1; }
class t extends u {}
$o = new t;
$o->y=2;
$o->var_dump($o);
$o->unset($o->y);
$o->var_dump($o);
$o->unset($o->x);
$o->var_dump($o);'
?>

Result:
object(t)#1 (2) {
["x"]=>
int(1)
["y"]=>
int(2)
}
object(t)#1 (0) {
}


With Patch:
object(t)#1 (2) {
["x"]=>
int(1)
["y"]=>
int(2)
}
object(t)#1 (1) {
["x"]=>
int(1)
}


Comments ?

Best regards,
Marcus                          mailto:helly@php.net

(Marcus Börger)

23 years ago

Hello Marcus,

Saturday, July 5, 2003, 4:16:03 PM, you wrote:

MB> Hello Zeev, hi Andi,

MB>   atm it is not possible to unset static members of a class which is correct
MB> since that would modify the class protocol. But it is possible to unset non
MB> dynamic properties (defined in the class). This should also be prevented as
MB> done with the attached patch.

MB> I did it by checking whether the name is part of the default properties. This
MB> works but maybe it is to slow. So perhaps it is a better solution to provide a
MB> flag in the property_info but then we#d have to do that in every class
MB> instantiation while my method would only take time when unset is used on
MB> props.

MB> Test code:
MB> <?php
MB> class u { var $x = 1; }
MB> class t extends u {}
MB> $o = new t;
$o->>y=2;
$o->>var_dump($o);
$o->>unset($o->y);
$o->>var_dump($o);
$o->>unset($o->x);
$o->>var_dump($o);'
?>>

MB> Result:
MB> object(t)#1 (2) {
MB>   ["x"]=>
MB>   int(1)
MB>   ["y"]=>
MB>   int(2)
MB> }
MB> object(t)#1 (0) {
MB> }


MB> With Patch:
MB> object(t)#1 (2) {
MB>   ["x"]=>
MB>   int(1)
MB>   ["y"]=>
MB>   int(2)
MB> }
MB> object(t)#1 (1) {
MB>   ["x"]=>
MB>   int(1)
MB> }


MB> Comments ?

During a nice chat with Andi both of us came to the conclusion that the user
may shoot himself in the knee if he wants to. So we allow unsetting default
properties what makes PHP objects a thing between real objects and pure
instances.

Best regards,
Marcus                            mailto:helly@php.net

Zeev Suraski

23 years ago

At 18:36 05/07/2003, Marcus Börger wrote:

>During a nice chat with Andi both of us came to the conclusion that the user
>may shoot himself in the knee if he wants to. So we allow unsetting default
>properties what makes PHP objects a thing between real objects and pure
>instances.

Just for the record, the pain involved in this shot won't be that
significant.  Because of the way the engine works, the access information
related to the property (PPP setting, whether it's static or not, etc.) are
kept separately, and won't be effected by unset().  So, if you unset a
private property, it still remains private, just without any value
currently attached to it.  It's really not that bad.

Zeev