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toString() and Object #ID

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Lars Schultz

19 years ago

Hi there

I just tried to switch from 5.1 to 5.2.3 and got thrown off right away by:
"Object of class MyObject could not be converted to string"

I googled a bit and also read any Messages in the internals list but
couldn't find a decisive answer as to wether this will stay this way or not.


In the "PHP 5 Bug Summary Report" I found Bug # 40799
"change string conversion behaviour for objects not implementing
__toString()"

which is still open. I don't want to complain or anything but I'd like
to know wether it's feasible to wait for a change in this current,
modified, behaviour or if it's going to stay this way.

I used the previous behaviour mostly for debugging purposes where I
wanted to get a visual (string) handle for any given object, which helps
ALOT when trying to figure out wether one has a copy or the original and
wether to references point to the same object....(obj1 === obj2 is not
always helpful). Is there any other way than casting an object to a
string to get an objects #ID?

Thanks for your time.
Lars

Evert | Rooftop

19 years ago

Hi Lars,

In the meanwhile .. check out spl_object_hash

Evert

Lars Schultz wrote:

Stanislav Malyshev

19 years ago

> always helpful). Is there any other way than casting an object to a
> string to get an objects #ID?

spl_object_hash?

--
Stanislav Malyshev, Zend Software Architect
stas@zend.com   http://www.zend.com/
(408)253-8829   MSN: stas@zend.com

Pavel Shevaev

19 years ago

On 6/30/07, Stanislav Malyshev <stas@zend.com> wrote:

> > always helpful). Is there any other way than casting an object to a
> > string to get an objects #ID?
>
> spl_object_hash?

Guys, excuse my being a little offtopic here, but why not introduce
standard "get_object_id" function in PHP6 which could be analogous to
"spl_object_hash"? IMHO it's a basic functionality which deserves to
be in the core...

--
Best regards, Pavel

Gwynne Raskind

19 years ago

On Jul 1, 2007, at 3:24 AM, Pavel Shevaev wrote:

>> > always helpful). Is there any other way than casting an object to a
>> > string to get an objects #ID?
>>
>> spl_object_hash?
> Guys, excuse my being a little offtopic here, but why not introduce
> standard "get_object_id" function in PHP6 which could be analogous to
> "spl_object_hash"? IMHO it's a basic functionality which deserves to
> be in the core...

+1 on PHP_FEALIAS()ing this.

-- Gwynne, Daughter of the Code
"This whole world is an asylum for the incurable."

Marcus Börger

19 years ago

Hello Gwynne,

no more unnecessary aliases please.

marcus

Sunday, July 1, 2007, 9:27:25 AM, you wrote:

> On Jul 1, 2007, at 3:24 AM, Pavel Shevaev wrote:
>>> > always helpful). Is there any other way than casting an object to a
>>> > string to get an objects #ID?
>>>
>>> spl_object_hash?
>> Guys, excuse my being a little offtopic here, but why not introduce
>> standard "get_object_id" function in PHP6 which could be analogous to
>> "spl_object_hash"? IMHO it's a basic functionality which deserves to
>> be in the core...

> +1 on PHP_FEALIAS()ing this.

> -- Gwynne, Daughter of the Code
> "This whole world is an asylum for the incurable."

Best regards,
Marcus

Sebastian Bergmann

19 years ago

Pavel Shevaev schrieb:

> Guys, excuse my being a little offtopic here, but why not introduce
> standard "get_object_id" function in PHP6 which could be analogous to
> "spl_object_hash"? IMHO it's a basic functionality which deserves to
> be in the core...

SPL is "in the core" AFAIAC.

--
Sebastian Bergmann                          http://sebastian-bergmann.de/
GnuPG Key: 0xB85B5D69 / 27A7 2B14 09E4 98CD 6277 0E5B 6867 C514 B85B 5D69

Pavel Shevaev

19 years ago

>
>  SPL is "in the core" AFAIAC.

I really want to hope it will be in PHP6. Still IMHO get_object_id
sounds much better than spl_object_hash and it will be much easier(and
more logical) to locate this function in "Class/Object Functions"
section of documentation than in SPL...

--
Best regards, Pavel

Marcus Börger

19 years ago

Hello Pavel,

technically object id is neither what you get nor what you want. It is not
unique and thus not helpfull and we have no intention to ever provide a
function to access it. See mail archieve for reference on why we won't.
Also the function resides in extension SPL so correctly it is prefixed with
'spl_'. Furthermore it is no engine specific function but an object oriented
programming specific one. So SPL indeed is a very good place for it. Lastly
the function per design hashes the unique input it gives as we do not want
to make it more complex than necessary or give you stuff that leads to
missuse. Again see mail archive for why. That said the name appears to be
the best option already.

marcus

Sunday, July 1, 2007, 1:42:02 PM, you wrote:

>>
>>  SPL is "in the core" AFAIAC.

> I really want to hope it will be in PHP6. Still IMHO get_object_id
> sounds much better than spl_object_hash and it will be much easier(and
> more logical) to locate this function in "Class/Object Functions"
> section of documentation than in SPL...

> --
> Best regards, Pavel

Best regards,
Marcus

Pavel Shevaev

19 years ago

> Again see mail archive for why. That said the name appears to be
> the best option already.

Oh, yes, you're right spl_object_hash does its job and does it very
well, there's really no point rename it(or make an alias) into
object_get_id. I should have stated more clear what I think
object_get_id could actually be.

How about object_get_id being a function returning the very first line
of var_dump's output being applied to the object? Let me be a bit more
specific, here's an example of var_dump usage:

$ php -r "class Foo{};$foo = new Foo();var_dump($foo);"
object(Foo)#1 (0) {
}

What I actually need, not the object hash but simply its unique id.
And in this case "object(Foo)#1" would be just fine. How can I get it?
The only way AFAIK is to surround var_dump with
ob_start/ob_get_contents/ob_end_clean functions and extract this
value.

The problem with approach is if one has a complex object connected
with a graph of other complex objects(with recursive links) var_dump
may take a _very_ long time to complete.
And this is what object_get_id could do - simply return object id
prefixed with the class name.

--
Best regards, Pavel

Lars Schultz

19 years ago

> What I actually need, not the object hash but simply its unique id.
> And in this case "object(Foo)#1" would be just fine. How can I get it?

That was my original Question too;) It's been stated that the automatic
cast into a string even if it does not implement the __toString()
function was "absolute nonsense"...but it really helped alot when you
needed to check for errors quickly and easily. Why make something harder
than it has to be.

Why not allow the old behaviour as long as the __toString is not
implemented? Or rather something like a default implementation which is
used autmatically for every class which doesn't implement it itself?

public function __toString(){
return 'Object '. get_class($this) .'('. get_object_id($this) .')';
}

That'd be nice and no code breakage would result. Isn't that an approach
that fits into the PHP philosophy? The new behaviour reminds me of
Java's "the more userland-code, the better".

Sebastian Bergmann

19 years ago

Pavel Shevaev schrieb:

> What I actually need, not the object hash but simply its unique id.

The problem is that there is no such unique id in the current engine.

--
Sebastian Bergmann                          http://sebastian-bergmann.de/
GnuPG Key: 0xB85B5D69 / 27A7 2B14 09E4 98CD 6277 0E5B 6867 C514 B85B 5D69

Lars Schultz

19 years ago

>  The problem is that there is no such unique id in the current engine.
>

Okay!;) That's a very good reason, I guess;) Explains a lot. Why not use
spl_object_hash instead of the old default behaviour?

Pavel Shevaev

19 years ago

>  The problem is that there is no such unique id in the current engine.

Am I right in my guess that there's only a counter for each object
type? Still being not really unique this information could be very
useful and enough in many situations.

--
Best regards, Pavel

David

19 years ago

(accidentally didn't send this to the whole group at first)

> Am I right in my guess that there's only a counter for each object
> type? Still being not really unique this information could be very
> useful and enough in many situations.

The "counter" is global, but it's not really a counter. "Object ids" are
actually handles (basically indices) into an internal array holding data to
all objects currently in memory. Handles are reused when an object is
destroyed so that the array could be kept as small as possible. However, if
you are comparing the handles of two objects that are known to be currently
in memory, if they have the same handle, then they are the same object (i.e.
one spot in memory).

However, if you stored the handle of the object in another area of memory so
that you can check it against other objects later, it's hard to ensure that
the results of that comparison is meaningful. Therefore, it's better to use
spl_object_hash to actually ensure objects are the same. Internally, the
hash is performed on the object handle (what you've been calling the "object
id") as well as the internal list of handlers for that object (basically the
"type" of the object), so there's reasonable confidence that a unique hash
will be generated. It looks like it's independent of the actual properties,
etc. of the object. Spl_object_hash is what you guys want.

David

Stanislav Malyshev

19 years ago

> Am I right in my guess that there's only a counter for each object
> type? Still being not really unique this information could be very
> useful and enough in many situations.

It's more complicated than that. Basically what uniquely identifies the
object is the tuple (handlers, ID) - it's more or less by definition
since handlers decide what to do with an object based on ID. Now, if we
talk about "pure" PHP objects (i.e. made by regular PHP user-defined
classes, no tricks) then the handlers would be the same and the ID is
unique. However, extensions can produce their own handlers and their own
IDs, and they don't even have to adhere to the concept that (class, ID)
should uniquely identify the object. I don't know of extension that
creates different handler sets for the same class, but there's nothing
in the engine preventing anybody from doing that - though I'm not sure
it's that good an idea.
So (class, ID) would probably work now, but is not guaranteed to work.
Just ID would have good chance to break with some extensions.

Yes, spl_object_hash uses the correct tuple - (handlers, ID).

--
Stanislav Malyshev, Zend Software Architect
stas@zend.com   http://www.zend.com/
(408)253-8829   MSN: stas@zend.com

Richard Lynch

19 years ago

On Sun, July 1, 2007 2:50 pm, Sebastian Bergmann wrote:

> Pavel Shevaev schrieb:
>> What I actually need, not the object hash but simply its unique id.
>
>  The problem is that there is no such unique id in the current engine.

How does PHP internally distinguish it?

Surely it has some kind of pointer/address thingie...

I don't think a developer CARES what the ID is (or isn't) or what it
looks like, so long as it's reasonably short and fast to access, and
it's not something that's only available sometimes on some systems.

--
Some people have a "gift" link here.
Know what I want?
I want you to buy a CD from some indie artist.
http://cdbaby.com/browse/from/lynch
Yeah, I get a buck. So?

David Zülke

19 years ago

Am 01.07.2007 um 21:18 schrieb Pavel Shevaev:

>> Again see mail archive for why. That said the name appears to be
>> the best option already.
>
> Oh, yes, you're right spl_object_hash does its job and does it very
> well, there's really no point rename it(or make an alias) into
> object_get_id. I should have stated more clear what I think
> object_get_id could actually be.

Not quite. It creates a hash of an object, so two objects with the
same data yield the same hashes:

var_dump(spl_object_hash(new stdClass()), spl_object_hash(new stdClass
()));


- David

Lars Schultz

19 years ago

> Not quite. It creates a hash of an object, so two objects with the
> same data yield the same hashes:
>
> var_dump(spl_object_hash(new stdClass()), spl_object_hash(new
> stdClass()));

I don't believe that it's data dependent. Rather in your example the
same memory-space is used for those two objects because they don't exist
in parallel. The first is cleared before the second is instantiated.

<?
$x = new stdClass();
$y = new stdClass();

var_dump(spl_object_hash($x), spl_object_hash($y));
?>

This yields a difference.

Pavel Shevaev

19 years ago

> The first is cleared before the second is instantiated.

Oh, that clears everything, please ignore my previous post. Still,
don't you think this is a bit misleading? IMHO, new object should
always have the unique id(or hash in terms of spl)...

--
Best regards, Pavel

Pavel Shevaev

19 years ago

> Not quite. It creates a hash of an object, so two objects with the
> same data yield the same hashes:
>
> var_dump(spl_object_hash(new stdClass()), spl_object_hash(new stdClass
> ()));

Folks, is this really wanted behavior? Because if so, why does the
following result in the same hash as well(PHP-5.2.1)?

$ php -r "class Foo{};$foo = new
Foo();var_dump(spl_object_hash($foo));$foo->bar =
1;var_dump(spl_object_hash($foo));"

string(32) "d1f40a1cc04d8c79d09ae6262666adbb"
string(32) "d1f40a1cc04d8c79d09ae6262666adbb"

>
> - David
>

--
Best regards, Pavel

Stephan Schmidt

19 years ago

Hi Pavel,

Pavel Shevaev wrote:

> Folks, is this really wanted behavior? Because if so, why does the
> following result in the same hash as well(PHP-5.2.1)?
>
> $ php -r "class Foo{};$foo = new
> Foo();var_dump(spl_object_hash($foo));$foo->bar =
> 1;var_dump(spl_object_hash($foo));"
>
> string(32) "d1f40a1cc04d8c79d09ae6262666adbb"
> string(32) "d1f40a1cc04d8c79d09ae6262666adbb"

Because you calculate the hash for the same object. It does not matter,
that you changed a property, the $foo is still the same object.

Best regards,
Stephan

Stanislav Malyshev

19 years ago

> Not quite. It creates a hash of an object, so two objects with the same
> data yield the same hashes:
>
> var_dump(spl_object_hash(new stdClass()), spl_object_hash(new stdClass()));

here's the code of spl_object_hash:


len = spprintf(&hash, 0, "%p:%d", Z_OBJ_HT_P(obj), Z_OBJ_HANDLE_P(obj));

md5str[0] = '\0';
PHP_MD5Init(&context);
PHP_MD5Update(&context, (unsigned char*)hash, len);
PHP_MD5Final(digest, &context);
make_digest(md5str, digest);
RETVAL_STRING(md5str, 1);

See any mention of object data? It's not there.

--
Stanislav Malyshev, Zend Software Architect
stas@zend.com   http://www.zend.com/
(408)253-8829   MSN: stas@zend.com

Richard Lynch

19 years ago

On Sun, July 1, 2007 2:18 pm, Pavel Shevaev wrote:

> $ php -r "class Foo{};$foo = new Foo();var_dump($foo);"
> object(Foo)#1 (0) {
> }
>
> What I actually need, not the object hash but simply its unique id.

According to Marcus, it's NOT unique.

But I can see that for debugging, it would be very very very useful to
have a correctly named function which returns this number, whatever it
is, even if it's not an ID.

--
Some people have a "gift" link here.
Know what I want?
I want you to buy a CD from some indie artist.
http://cdbaby.com/browse/from/lynch
Yeah, I get a buck. So?

Marcus Börger

19 years ago

Hello Pavel,

I still fail to understand why spl_object_hash() does not work for you.
How about:

function foo($obj) {
if (is_object($obj)) {
return "object(" . get_class($obj) . ")#" . spl_object_hash($obj);
}
return NULL;
}

marcus

Sunday, July 1, 2007, 9:18:19 PM, you wrote:

>> Again see mail archive for why. That said the name appears to be
>> the best option already.

> Oh, yes, you're right spl_object_hash does its job and does it very
> well, there's really no point rename it(or make an alias) into
> object_get_id. I should have stated more clear what I think
> object_get_id could actually be.

> How about object_get_id being a function returning the very first line
> of var_dump's output being applied to the object? Let me be a bit more
> specific, here's an example of var_dump usage:

> $ php -r "class Foo{};$foo = new Foo();var_dump($foo);"
> object(Foo)#1 (0) {
> }

> What I actually need, not the object hash but simply its unique id.
> And in this case "object(Foo)#1" would be just fine. How can I get it?
> The only way AFAIK is to surround var_dump with
> ob_start/ob_get_contents/ob_end_clean functions and extract this
> value.

> The problem with approach is if one has a complex object connected
> with a graph of other complex objects(with recursive links) var_dump
> may take a _very_ long time to complete.
> And this is what object_get_id could do - simply return object id
> prefixed with the class name.

Best regards,
Marcus

Cristian Rodriguez

19 years ago

On 6/29/07, Lars Schultz <schultz@widescreen.ch> wrote:

> Hi there
>
> I just tried to switch from 5.1 to 5.2.3 and got thrown off right away by:
> "Object of class MyObject could not be converted to string"
>
> I googled a bit and also read any Messages in the internals list but
> couldn't find a decisive answer as to wether this will stay this way or not.
>
>
> In the "PHP 5 Bug Summary Report" I found Bug # 40799
> "change string conversion behaviour for objects not implementing
> __toString()"
>
> which is still open. I don't want to complain or anything but I'd like
> to know wether it's feasible to wait for a change in this current,
> modified, behaviour or if it's going to stay this way.

The old beahviuor was absolute non-sense..

> always helpful). Is there any other way than casting an object to a
> string to get an objects #ID?
>

use var_dump() or spl_object_hash for that.