Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:102646
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 209.85.218.51 as permitted sender)
MIME-Version: 1.0
Sender: nicolas.grekas@gmail.com
In-Reply-To: <CAF+90c8k2rmh8V7yfKOFA57ft1cNjz3DeT-V1LHsnaJnn0XEKg@mail.gmail.com>
References: <CAF+90c8k2rmh8V7yfKOFA57ft1cNjz3DeT-V1LHsnaJnn0XEKg@mail.gmail.com>
Date: Sun, 8 Jul 2018 10:42:08 +0200
Message-ID: <CAOWwgpn-7psj9HCFzEJgRg1FvyC7V+AYK5bduNoWgdC8q+fJCg@mail.gmail.com>
To: Nikita Popov <nikita.ppv@gmail.com>
Cc: PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000873dbf057078e099"
Subject: Re: [PHP-DEV] Introspection for references
From: nicolas.grekas+php@gmail.com (Nicolas Grekas)

--000000000000873dbf057078e099
Content-Type: text/plain; charset="UTF-8"

Hi Nikita,


Before talking about solutions, can the people who need this first outline
> what functionality is needed and what it is needed for (and maybe what
> workarounds you currently use). E.g. do you only need to know whether
> something is a reference, or do you need to know whether two somethings are
> part of the same reference, etc. There are probably multiple use cases for
> this with different needs.
>

We're using reference introspection to do both: we need to know when a zval
is a reference, and we also need to track each of them separately.

The use case is being able to intropect any arbitrary PHP datastructure,
with one main application: providing an enhanced "dump()" function.

See e.g. this screenshot for what we get using the dump() function provided
by Symfony VarDumper component:
https://symfony.com/doc/current/_images/07-hard-ref.png

In PHP5 days, Julien Pauli wrote a PHP extension to do zval introspection.
Here is the code + README (see test case 001.phpt for example with
references.):
https://github.com/symfony/symfony/tree/3.4/src/Symfony/Component/Debug/Resources/ext

With PHP7, using pure PHP introspection is easier to maintain and still
very fast so we deprecated the extension.
Here is the code doing reference introspection:
https://github.com/symfony/symfony/blob/master/src/Symfony/Component/VarDumper/Cloner/VarCloner.php#L83

it might not be easy to follow, but the basic blocks are:

$array2 = $array1;
$array2[$key] = $unique_cookie;
if ($array1[$key] === $unique_cookie) => we found a reference
then we also maintain a registry of $unique_cookie so that we know if we
already saw that reference or not (the check is done before the above "if"
or course.)

Cheers,
Nicolas

--000000000000873dbf057078e099--