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Date: Mon, 3 Aug 2015 09:20:18 +0200
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To: Rowan Collins <rowan.collins@gmail.com>
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Subject: Re: [PHP-DEV] Exposing object handles to userland
From: nicolas.grekas+php@gmail.com (Nicolas Grekas)

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2015-08-02 20:03 GMT+02:00 Rowan Collins <rowan.collins@gmail.com>:

> On 02/08/2015 18:41, Bob Weinand wrote:
>
>> Some suspicious use of spl_object_hash() out there...
>>> >
>>>
>>>> >>
>>>> https://github.com/symfony/symfony/blob/master/src/Symfony/Component/V=
arDumper/Cloner/VarCloner.php
>>>>
>>> >
>>> >Not sure what this one does... but calculations with spl_object_hash()
>>> >look very suspicious.
>>>
>> Actually, it's doing the right thing=E2=80=A6 calculating the value the =
object id
>> is xor'ed with (as we know that consecutively defined objects have
>> consecutive ids).
>> It's relying on the implementation of spl_object_hash() and will even
>> continue to work when we remove that part of randomness as that value it=
's
>> xor'ed with is then nothing else than 0.
>>
>
> The right thing for what purpose? Why does it need that ID, rather than
> the value that spl_object_hash() gave in the first place? Just to be
> prettier to the user?
>


For the purpose of providing an id that humans can read and compare, to
easily spot if two objects are identical or not. Try comparing two
spl_object_hashes and you'll understand the need...

The id as displayed by e.g. var_dump is not an implementation detail that
leaks through it.
It's really an important feature of the output.

I learned that while implementing VarDumper (see link above), by user
requests.

Regards,
Nicolas

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