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From: Daniel Kolbo on 11 Jul 2010 18:19
Hello PHPers,

I'm having some trouble understanding some PHP behaviour. The following
example script exhibits the behaviour which I cannot understand.
[code]
<?php

class A
{
public static $a = 3;

function __construct()
{
//self::$a = $this; //[i]
self::$a =& $this; //[ii]
}
}

class B extends A
{
function __construct()
{
parent::__construct();
}
}

class C {
var $c;

function __construct()
{
$this->c =& A::$a;
}

}


$c = new C;
$b = new B;
$cee = new C;

var_dump($c->c); // [i] prints object(B), but [ii] prints int 3
var_dump($cee->c); // [i] prints object(B), and [ii] prints object(B)

?>
[/code]

Why does $c->c print 'int 3' ?

I'm nervous to use "self::$a = $this;" because I don't want to be
copying the whole object. However, isn't $this just a reference to the
object, so "self::$a = $this;" is just copying the reference and not the
actual object, right?

Thanks in advance
`
From: Richard Quadling on 12 Jul 2010 07:00
On 11 July 2010 23:19, Daniel Kolbo <kolb0057(a)umn.edu> wrote:
> Hello PHPers,
>
> I'm having some trouble understanding some PHP behaviour.  The following
> example script exhibits the behaviour which I cannot understand.
> [code]
> <?php
>
> class A
> {
>        public static $a = 3;
>
>        function __construct()
>        {
>                //self::$a = $this; //[i]
>                self::$a =& $this; //[ii]
>        }
> }
>
> class B extends  A
> {
>        function __construct()
>        {
>                parent::__construct();
>        }
> }
>
> class C {
>        var $c;
>
>        function __construct()
>        {
>                $this->c =& A::$a;
>        }
>
> }
>
>
> $c = new C;
> $b = new B;
> $cee = new C;
>
> var_dump($c->c); // [i] prints object(B), but [ii] prints int 3
> var_dump($cee->c); // [i] prints object(B), and [ii] prints object(B)
>
> ?>
> [/code]
>
> Why does $c->c print 'int 3' ?
>
> I'm nervous to use "self::$a = $this;" because I don't want to be
> copying the whole object.  However, isn't $this just a reference to the
> object, so "self::$a = $this;" is just copying the reference and not the
> actual object, right?
>
> Thanks in advance


What do you think the value should be?

A static property is bound to the class and not to an instance of the class..

So, &A::$a is a reference to the static value. If you alter the value,
it will be altered for a subclasses of A and for any other reference
to it.
From: Daniel Kolbo on 12 Jul 2010 17:54
Richard Quadling wrote:
> On 11 July 2010 23:19, Daniel Kolbo <kolb0057(a)umn.edu> wrote:
>> Hello PHPers,
>>
>> I'm having some trouble understanding some PHP behaviour. The following
>> example script exhibits the behaviour which I cannot understand.
>> [code]
>> <?php
>>
>> class A
>> {
>> public static $a = 3;
>>
>> function __construct()
>> {
>> //self::$a = $this; //[i]
>> self::$a =& $this; //[ii]
>> }
>> }
>>
>> class B extends A
>> {
>> function __construct()
>> {
>> parent::__construct();
>> }
>> }
>>
>> class C {
>> var $c;
>>
>> function __construct()
>> {
>> $this->c =& A::$a;
>> }
>>
>> }
>>
>>
>> $c = new C;
>> $b = new B;
>> $cee = new C;
>>
>> var_dump($c->c); // [i] prints object(B), but [ii] prints int 3
>> var_dump($cee->c); // [i] prints object(B), and [ii] prints object(B)
>>
>> ?>
>> [/code]
>>
>> Why does $c->c print 'int 3' ?
>>
>> I'm nervous to use "self::$a = $this;" because I don't want to be
>> copying the whole object. However, isn't $this just a reference to the
>> object, so "self::$a = $this;" is just copying the reference and not the
>> actual object, right?
>>
>> Thanks in advance
>
>
> What do you think the value should be?
>
> A static property is bound to the class and not to an instance of the class.
>
> So, &A::$a is a reference to the static value. If you alter the value,
> it will be altered for a subclasses of A and for any other reference
> to it.
>

I think
var_dump($c->c); would print object(B), but it's printing int 3.

The reference is *not* being updated. I think this is a bug. What do
you think?

Thanks
`

From: Richard Quadling on 13 Jul 2010 04:46
On 12 July 2010 22:54, Daniel Kolbo <kolb0057(a)umn.edu> wrote:
> Richard Quadling wrote:
>> On 11 July 2010 23:19, Daniel Kolbo <kolb0057(a)umn.edu> wrote:
>>> Hello PHPers,
>>>
>>> I'm having some trouble understanding some PHP behaviour.  The following
>>> example script exhibits the behaviour which I cannot understand.
>>> [code]
>>> <?php
>>>
>>> class A
>>> {
>>>        public static $a = 3;
>>>
>>>        function __construct()
>>>        {
>>>                //self::$a = $this; //[i]
>>>                self::$a =& $this; //[ii]
>>>        }
>>> }
>>>
>>> class B extends  A
>>> {
>>>        function __construct()
>>>        {
>>>                parent::__construct();
>>>        }
>>> }
>>>
>>> class C {
>>>        var $c;
>>>
>>>        function __construct()
>>>        {
>>>                $this->c =& A::$a;
>>>        }
>>>
>>> }
>>>
>>>
>>> $c = new C;
>>> $b = new B;
>>> $cee = new C;
>>>
>>> var_dump($c->c); // [i] prints object(B), but [ii] prints int 3
>>> var_dump($cee->c); // [i] prints object(B), and [ii] prints object(B)
>>>
>>> ?>
>>> [/code]
>>>
>>> Why does $c->c print 'int 3' ?
>>>
>>> I'm nervous to use "self::$a = $this;" because I don't want to be
>>> copying the whole object.  However, isn't $this just a reference to the
>>> object, so "self::$a = $this;" is just copying the reference and not the
>>> actual object, right?
>>>
>>> Thanks in advance
>>
>>
>> What do you think the value should be?
>>
>> A static property is bound to the class and not to an instance of the class.
>>
>> So, &A::$a is a reference to the static value. If you alter the value,
>> it will be altered for a subclasses of A and for any other reference
>> to it.
>>
>
> I think
> var_dump($c->c); would print object(B), but it's printing int 3.
>
> The reference is *not* being updated.  I think this is a bug.  What do
> you think?
>
> Thanks
> `
>
>

What version of PHP are you using?
From: Richard Quadling on 13 Jul 2010 04:59
On 13 July 2010 09:46, Richard Quadling <rquadling(a)gmail.com> wrote:
> On 12 July 2010 22:54, Daniel Kolbo <kolb0057(a)umn.edu> wrote:
>> Richard Quadling wrote:
>>> On 11 July 2010 23:19, Daniel Kolbo <kolb0057(a)umn.edu> wrote:
>>>> Hello PHPers,
>>>>
>>>> I'm having some trouble understanding some PHP behaviour.  The following
>>>> example script exhibits the behaviour which I cannot understand.
>>>> [code]
>>>> <?php
>>>>
>>>> class A
>>>> {
>>>>        public static $a = 3;
>>>>
>>>>        function __construct()
>>>>        {
>>>>                //self::$a = $this; //[i]
>>>>                self::$a =& $this; //[ii]
>>>>        }
>>>> }
>>>>
>>>> class B extends  A
>>>> {
>>>>        function __construct()
>>>>        {
>>>>                parent::__construct();
>>>>        }
>>>> }
>>>>
>>>> class C {
>>>>        var $c;
>>>>
>>>>        function __construct()
>>>>        {
>>>>                $this->c =& A::$a;
>>>>        }
>>>>
>>>> }
>>>>
>>>>
>>>> $c = new C;
>>>> $b = new B;
>>>> $cee = new C;
>>>>
>>>> var_dump($c->c); // [i] prints object(B), but [ii] prints int 3
>>>> var_dump($cee->c); // [i] prints object(B), and [ii] prints object(B)
>>>>
>>>> ?>
>>>> [/code]
>>>>
>>>> Why does $c->c print 'int 3' ?
>>>>
>>>> I'm nervous to use "self::$a = $this;" because I don't want to be
>>>> copying the whole object.  However, isn't $this just a reference to the
>>>> object, so "self::$a = $this;" is just copying the reference and not the
>>>> actual object, right?
>>>>
>>>> Thanks in advance
>>>
>>>
>>> What do you think the value should be?
>>>
>>> A static property is bound to the class and not to an instance of the class.
>>>
>>> So, &A::$a is a reference to the static value. If you alter the value,
>>> it will be altered for a subclasses of A and for any other reference
>>> to it.
>>>
>>
>> I think
>> var_dump($c->c); would print object(B), but it's printing int 3.
>>
>> The reference is *not* being updated.  I think this is a bug.  What do
>> you think?
>>
>> Thanks

Aha!

$c = new C;

At this stage $c->c will be a reference to the static A::$a = 3.

$b = new B;

Now, as B's constructor calls A's constructor which replaces the
static A::$a with a reference to the instance $b, the static A::$a
should now be $b

$cee = new C;

At this stage $cee->c will be a reference to the static A::$a = $b.

But, when var_dump()'d, $c->c !== $cee->c, and I think they should as
both have been assigned to a reference of a static.

It would seem to be a bug.

I get the same output for V5.0.0 to V5.3.3RC2
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