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php

Pass source object to clone like __clone($origThis)

php.internals

Michael Voříšek - ČVUT FEL

6 years ago

Hi, please look at
https://stackoverflow.com/questions/63675888/get-original-source-instance-in-clone


do you have anything against updating PHP to pass "instance before
cloned" to any __clone call from php?

no BC - user may accept this extra argument or declare function
__clone() without any param like now

With kind regards / Mit freundlichen Grüßen / S přátelským pozdravem,

Michael Voříšek

David Rodrigues

6 years ago

I understand... seems that `$this` is very confusing inside `__clone()`:
when writing, it writes to the clone, when reading it reads from original.

Seems valid a new optional parameter definition with the original source.

Atenciosamente,
David Rodrigues

Em qua., 2 de set. de 2020 às 15:41, Michael Voříšek - ČVUT FEL <
vorismi3@fel.cvut.cz> escreveu:

Sara Golemon

6 years ago

On Wed, Sep 2, 2020 at 2:11 PM David Rodrigues <david.proweb@gmail.com>
wrote:

> I understand... seems that `$this` is very confusing inside `__clone()`:
> when writing, it writes to the clone, when reading it reads from original.
>
>

That's not an accurate description of what happens today.

$newObj = clone $oldObj;
// 1. Engine creates a new instance of get_class($oldObj), without calling
the constructor
// 2. Engine copies all properties from the old object to the new object
// 3. Engine invokes $newObj->__clone()
public function __clone() {
// Userspace object handles any property specific re-initialization
required.
// $this always refers to the new object here.
}

The question Niki asked is appropriate; What would one want to do to
$oldObj here?
If the goal is to read from the old object, then you have that already.
The new object is a perfect copy, so read from that.
If the goal is to write to the old object, then justify why you need to do
so, because it's not a clone operation at that point.

-Sara

David Rodrigues

5 years ago

Now I rethinked about what I said. Really, maybe clone is not the best
option. So maybe we can just use a method that will clone and will have
access to both informations. But I don't know if it solves the original
message.

public function getUserCopy() {
$userCopy = clone $this;
$this->copies[] = $userCopy;

return $userCopy;
}

Considering it, we have access to both now, with "write to source" support
with no additional feature need.

Em qui, 3 de set de 2020 11:21, Sara Golemon <pollita@php.net> escreveu:

Sara Golemon

5 years ago

On Thu, Sep 3, 2020 at 10:40 AM David Rodrigues <david.proweb@gmail.com>
wrote:

> Now I rethinked about what I said. Really, maybe clone is not the best
> option. So maybe we can just use a method that will clone and will have
> access to both informations. But I don't know if it solves the original
> message.
>
> public function getUserCopy() {
>     $userCopy = clone $this;
>     $this->copies[] = $userCopy;
>
>     return $userCopy;
> }
>
>

If your goal is to track copies, then a static makes much more sense.

class AllKnowing {
private static $copies = [];

public function __construct(...) {
self::$copies[] = $this;
....
}

public function __clone() {
self::$copies[] = $this;
}
}

-Sara

David Rodrigues

5 years ago

It was just an example to avoid modify how clone works, using existing
features. :)

Em qui, 3 de set de 2020 13:00, Sara Golemon <pollita@php.net> escreveu:

Sara Golemon

5 years ago

On Thu, Sep 3, 2020 at 11:03 AM David Rodrigues <david.proweb@gmail.com>
wrote:

> It was just an example to avoid modify how clone works, using existing
> features. :)

>

Right, but the question remains "Why would we want the original object
during a clone operation?".  No legitimate example of that has been
provided yet.

-Sara

Michael Voříšek - ČVUT FEL

5 years ago

The goal is to be able to access the original object and it's id/hash.

Usecases:

- something is associated with the object using the object id/hash and
it needs to be cloned as well

we need the original object to obtain it's id/hash for spl_object_id and
spl_object_hash methods

- bounded Closures ar associated with the original object and they needs
to be rebound to the cloned object

example:

public function __clone(self $origThis)
{
if ((new \ReflectionFunction($this->fx))->getClosureThis() ===
$origThis) {
$this->fx = \Closure::bind($this->fx, $this);
}
}

Modification of php is simple:

https://github.com/php/php-src/pull/6063/files#diff-beea8c5a8ceb318220b34b73e4ecfc98R252


we simply pass the old object as 1 parameter. I belive, passing old
object have positives and no performance nor compatibility impact. All
other current solutions require an extra property and a lot of code, as
assigning in constructor is not enough (due serialization etc.), or it
is even impossible, if object was created using reflection without
constructor.

With kind regards / Mit freundlichen Grüßen / S přátelským pozdravem,

Michael Voříšek

On 3 Sep 2020 18:00, Sara Golemon wrote:

David Rodrigues

5 years ago

Just to I know, it can't be done by an intermediary method like my previous
example? Why are the limitations to that?

About PR, could you provide some additional tests?

Thanks!

Em qui, 3 de set de 2020 13:37, Michael Voříšek - ČVUT FEL <
vorismi3@fel.cvut.cz> escreveu:

Nikita Popov

6 years ago

On Wed, Sep 2, 2020 at 8:42 PM Michael Voříšek - ČVUT FEL <
vorismi3@fel.cvut.cz> wrote:

> Hi, please look at
>
> https://stackoverflow.com/questions/63675888/get-original-source-instance-in-clone
>
>
> do you have anything against updating PHP to pass "instance before
> cloned" to any __clone call from php?
>
> no BC - user may accept this extra argument or declare function
> __clone() without any param like now
>

Could you please provide some more information on what the intended
use-case is?

I'm not opposed to this change, but I also don't understand why it is
needed.

Regards,
Nikita

Pedro Magalhães

6 years ago

On Wed, Sep 2, 2020 at 7:41 PM Michael Voříšek - ČVUT FEL <
vorismi3@fel.cvut.cz> wrote:

> do you have anything against updating PHP to pass "instance before
> cloned" to any __clone call from php?
>

Yes, I think that allowing the original object to be modified by a cloning
operation could be the cause for a lot of confusion. If we had a proper way
to make it read-only I wouldn't mind, but as is, it doesn't sound like a
good idea.

David Rodrigues

6 years ago

I don't see problem to allow modify the original object, once that you are
doing it by using a new argument, and not the $this itself.

Em qui, 3 de set de 2020 08:49, Pedro Magalhães <mail@pmmaga.net> escreveu: