Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:70535
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 74.125.82.52 as permitted sender)
Message-ID: <52A4A6A1.3080206@gmail.com>
Date: Sun, 08 Dec 2013 17:04:33 +0000
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.1
MIME-Version: 1.0
To: PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative;
 boundary="------------040105050805070409090000"
Subject: Introducing pragmas into PHP?
From: ellison.terry@gmail.com (Terry Ellison)

--------------040105050805070409090000
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Hi,

We have ongoing debates about the pull between BC behaviour and wanting 
to tidy up / optimize performance etc.  And often BC for bizarre coding 
practices means that there is a performance penalty for everyone else.  
A common way of doing this in C etc. is the use of compiler pragmas, but 
such a change would in itself be not BC and INI parameters are too blunt 
an instrument here as these are set at runtime or globally as a 
PER_INI_USER etc. They can't impact the current source being compiled, 
and they can't be conveniently namespace-specific.

I am suggestion the overload of constants of the form PHP_PRAGMA_XXX to 
define PHP / Zend compiler / executor behaviours. This approach would be 
BC to 5.3 unless, of course, the application already used PHP_PRAGMA_* 
constants, in which case we might also need an allow_php_pragmas INI 
parameter to globally enable/disable their interpretation.

As a small example:

    namespace fred;
    echo \strlen("DDDD");

generates different .

    SEND_VAL                            'DDDD'
    DO_FCALL                 1  $0      'strlen'

and different (slower) opcode if you omit the \

    INIT_NS_FCALL_BY_NAME               'strlen'
    SEND_VAL                            'DDDD'
    DO_FCALL_BY_NAME         1  $0

Whilst most sane projects would have a simple programming standard which 
basically says "Don't override builtin functions", the odd one might for 
various reasons allow this.  This practice can significantly complicate 
optimization for performance (see 
https://bugs.php.net/bug.php?id=64346).  I've seen namespace-based 
project where all builtins have the explicit global \ prefix.  IMO, yukkk.

So my suggestion is that we allow the programmer to issue a pragma to 
inform compiler and runtime handling, so in this case for example,

    namespace fred;
    const PHP_PRAGMA_ALLOW_OVERRIDE_BUILTINS=false;
    echo strlen("DDDD");

would define the constant fred\PHP_PRAGMA_ALLOW_OVERRIDE_BUILTINS and 
also have the desired compile-time and runtime effect. Alternatively the 
corresponding global constant \PHP_PRAGMA_ALLOW_OVERRIDE_BUILTINS could 
be set to false and individual namespaces could set the corresponding 
namespace constant to true.

Thoughts and comments?

Terry Ellison

--------------040105050805070409090000--