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Date: Thu, 21 Aug 2014 10:28:59 -0700
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To: Derick Rethans <derick@php.net>
Cc: PHP Developers Mailing List <internals@lists.php.net>
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Subject: Re: [PHP-DEV] On BC and not being evil (Was: Re: [PHP-DEV] [RFC]
 Integer Semantics)
From: aharvey@php.net (Adam Harvey)

On 21 August 2014 08:30, Derick Rethans <derick@php.net> wrote:
> Can I please urge people to not take Backwards Compatibility issues so
> lightly. Please think really careful when you suggest to break Backwards
> Compatibility, it should only be considered if there is a real and
> important reason to do so. Changing binary comparison is not one of
> those, changing behaviour for everybody regarding ``<<`` and ``>>`` is
> not one of those, and subtle changes to what syntax means is certainly
> not one of them.
>
> **Don't be Evil**

+1 on everything Derick said.

I want to make one more point: if there's just one thing we learn from
other languages that have made BC-breaking, major version transitions,
it should be that library and framework authors will ultimately have
to support both versions in the same code base. Python tried using
tooling such as 2to3 to help manage the transition, but in the end the
only way Python 3 has gotten any traction is libraries supporting
both, which effectively means that library authors can only write the
subset of Python that's supported by 2 and 3.

Every time we break BC =E2=80=94 in either of the ways Derick said =E2=80=
=94 we narrow
the subset of PHP 5 and PHP 7 that's available to people writing PHP
code that has to work on both. If we narrow it too far, it'll be too
unexpressive, or too hard to use, or just plain won't do something
that they'll need, and PHP 7 will risk becoming this decade's Perl 6:
the cautionary tale for what happens when you burn all the boats.

PHP 7 is an opportunity. It needs to be one that we embrace, and take
advantage of, but most importantly one that is evolutionary and allows
our user base to come with us.

Adam