php-general Digest 14 Jul 2010 09:10:44 -0000 Issue 6845
Topics (messages 306882 through 306886):
Re: Static Class Member References
306882 by: Daniel Kolbo
306883 by: Daniel Kolbo
306886 by: Ford, Mike
Re: Posting values of dynamically generated text fields at a time
306884 by: Saravanan Murugesan
306885 by: Ashley Sheridan
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----------------------------------------------------------------------
--- Begin Message ---
Richard Quadling wrote:
> On 12 July 2010 22:54, Daniel Kolbo <[email protected]> wrote:
>> Richard Quadling wrote:
>>> On 11 July 2010 23:19, Daniel Kolbo <[email protected]> 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?
>
I'm using:
PHP Version 5.2.13
--- End Message ---
--- Begin Message ---
Richard Quadling wrote:
> On 13 July 2010 09:46, Richard Quadling <[email protected]> wrote:
>> On 12 July 2010 22:54, Daniel Kolbo <[email protected]> wrote:
>>> Richard Quadling wrote:
>>>> On 11 July 2010 23:19, Daniel Kolbo <[email protected]> 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 !== $cee->c, and I think they should as
> both have been assigned to a reference of a static.
>
> It would seem to be a bug.
>
> I get the same output for V5.0.0 to V5.3.3RC2
>
Thanks for confirming. I reported the bug. I shortened up the test
script quite a bit. Please see: Bug #52332
http://bugs.php.net/bug.php?id=52332
`
--- End Message ---
--- Begin Message ---
> -----Original Message-----
> From: Daniel Kolbo [mailto:[email protected]]
> Sent: 11 July 2010 23:19
>
> Hello PHPers,
>
> I'm having some trouble understanding some PHP behaviour. The
> following
> example script exhibits the behaviour which I cannot understand.
I'm pretty sure that this is *not* a bug. I'll answer your last
question first, and then demonstrate with your code.
> I'm nervous to use "self::$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?
Not exactly, although everybody seems to refer to it as a reference
for convenience. Most of the time it doesn't matter, but when you
start introducing references to objects it can - it's better to think
of an object variable as holding the object's *handle*
(see http://php.net/anguage.oop5.references.php for more on this), so
it's clear exactly what a reference is referencing.
Now for your code:
> [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;
[i] & [ii] in C::__construct(): $c->c = reference to same value as
A::$a (currently (int)3)
NOTE: because of how references work, A::$a is now also a
reference to (int)3.
> $b = new B;
[i] in A::__construct(): A::$a = handle of object B(1) (also assigned to
global $b)
NOTE: $c->c, as reference to $A::a, now also references handle of
object B(1)
[ii] in A::__construct(): A::$a = reference to handle of object B(1)
NOTE: since we are assigning a new reference to a variable which is
already a reference, ONLY this reference changes -- so $c->c
is still a reference to (int)3...!
> $cee = new C;
Irrelevant -- the damage has already been done!
> var_dump($c->c); // [i] prints object(B), but [ii] prints int 3
> var_dump($cee->c); // [i] prints object(B), and [ii] prints
> object(B)
... which is correct according to my interpretation.
This has been such a regular confusion, that some time ago I wrote
this test script:
<?php
class test {
public $me;
}
$t = new test;
$t->me = 'Original';
$copy_t = $t;
$ref_t = &$t;
$copy_t = new test;
$copy_t->me = 'Altered Copy';
echo <<<RESULT1
Original: $t->me<br />
Copy: $copy_t->me<br />
Reference: $ref_t->me<br />
RESULT1;
$ref_t = new test;
$ref_t->me = 'Altered Reference';
echo <<<RESULT2
<br />
Original: $t->me<br />
Copy: $copy_t->me<br />
Reference: $ref_t->me<br />
RESULT2;
$s = 'String';
$copy_s = $s;
$ref_s = &$s;
$copy_s = 'String Copy';
echo <<<RESULT3
<br />
Original: $s<br />
Copy: $copy_s<br />
Reference: $ref_s<br />
RESULT3;
$ref_s = 'String Reference';
echo <<<RESULT4
<br />
Original: $s<br />
Copy: $copy_s<br />
Reference: $ref_s<br />
RESULT4;
?>
Which gives this output:
Original: Original
Copy: Altered Copy
Reference: Original
Original: Altered Reference
Copy: Altered Copy
Reference: Altered Reference
Original: String
Copy: String Copy
Reference: String
Original: String Reference
Copy: String Copy
Reference: String Reference
Which demonstrates how exactly the behaviour of objects correlates to
scalars with regards to copying and referencing -- but may not be
exactly what you expect if you think of object variables as always
holding a reference to the object. I would heartily recommend always
to think of an object variable as holding the object's *handle*, and
*not* a reference - this may croggle your brain a bit, but makes it a
Lot clearer what's happening in edge cases like this.
Cheers!
Mike
--
Mike Ford,
Electronic Information Developer, Libraries and Learning Innovation,
Leeds Metropolitan University, C507, Civic Quarter Campus,
Woodhouse Lane, LEEDS, LS1 3HE, United Kingdom
Email: [email protected]
Tel: +44 113 812 4730
To view the terms under which this email is distributed, please go to
http://disclaimer.leedsmet.ac.uk/email.htm
--- End Message ---
--- Begin Message ---
> Hi is anybody there to help me out on this?????
>
>>
>> Hi all,
>> I am new to PHP and JS.
>>
>> I am adding new text fields using javascript and I have to save the
>> values
>> of these fields in database in single row. So, how should I post these
>> values? So that I can save them in the db.
>>
>> Additional Info: There are 6 text fields in the row. I have to post the
>> information of all the fields collectively.
>>
>> So, please suggest me a way.........
>> --
>> Thanks and Regards,
>> Amit
>>
>>
>
>
> --
> Thanks and Regards,
> Amit
> eArth Solutions Pvt. Ltd
>
Hi,
this would help you,
http://www.w3schools.com/PHP/php_mysql_insert.asp
Thanks,
Saravana
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--- End Message ---
--- Begin Message ---
On Wed, 2010-07-14 at 12:08 +0530, Saravanan Murugesan wrote:
> > Hi is anybody there to help me out on this?????
> >
> >>
> >> Hi all,
> >> I am new to PHP and JS.
> >>
> >> I am adding new text fields using javascript and I have to save the
> >> values
> >> of these fields in database in single row. So, how should I post these
> >> values? So that I can save them in the db.
> >>
> >> Additional Info: There are 6 text fields in the row. I have to post the
> >> information of all the fields collectively.
> >>
> >> So, please suggest me a way.........
> >> --
> >> Thanks and Regards,
> >> Amit
> >>
> >>
> >
> >
> > --
> > Thanks and Regards,
> > Amit
> > eArth Solutions Pvt. Ltd
> >
>
> Hi,
>
> this would help you,
> http://www.w3schools.com/PHP/php_mysql_insert.asp
>
> Thanks,
> Saravana
>
>
> ===========================================================
> ***Disclaimer***
>
>
> This email, and any attachments ("this email"), is confidential. If you are
> not the addressee
> please tell the sender immediately, and destroy this email without using,
> sending or storing
> it. Any opinions, express or implied, in this email, are those of the sender,
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> necessarily approved by Hurix Systems. Except as expressly stated, this
> e-mail should not be
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> accept liability
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>
> HURIX SYSTEMS MAY MONITOR ALL INCOMING AND OUTGOING MAILS
> ============================================================
>
Erm, that's not even remotely an answer to the OPs question...
Thanks,
Ash
http://www.ashleysheridan.co.uk
--- End Message ---
