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Date: Sun, 3 Feb 2013 23:22:17 +0100
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To: Karoly Negyesi <karoly@negyesi.net>
Cc: "internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Proposal for serious BC compatibility aka language versioning
From: nikita.ppv@gmail.com (Nikita Popov)

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On Sun, Feb 3, 2013 at 12:36 PM, Karoly Negyesi <karoly@negyesi.net> wrote:

> Hi,
>
> So, if we are talking about PHP 6, then the opening <?php tag should be
> accompanied by the version it was written for, it was tested with and then
> the engine could switch to a compatibility mode for that version.
>
> Seems to me that this would solve the problem where a host can't upgrade to
> a more modern version for fear of breaking old code. Consequently, open
> source packages -- like Drupal I am deeply involved with -- can't use more
> modern PHP versions decreasing the "push" for hosts to upgrade. This is a
> devilish circle and it'd be great to break it.
>
> Regards,
>
> Karoly Negyesi
>

At least two points why this makes no sense whatsoever:

1) One would have to maintain or at least keep around all previous versions
of the engine and the libraries. That would be a shitload of cruft and a
lot of maintenance work.

2) Different behavior per-file is not feasible as components in both files
interact. If you have one <?php6 file and one <?php5 file and both interact
(like, you know, calling a function from one file in the other one) you
will have a pretty hard time decided what behavior this should result in.
The <?php6 behavior or the <?php5 one? So something like this can only be
done on a per-request basis (rather than per-file). And to do this on a
per-request basis you already have all the means. Just run two different
PHP versions. No issue with that; doesn't require no further support from
PHP.

Nikita

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