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Date: Tue, 20 Aug 2024 19:04:39 +0200
Message-ID: <CAPyj-LCRfvPvZcJmE=afc9CGK-mvbXDRvzOTxrr_nfLk2LghQQ@mail.gmail.com>
Subject: Re: [PHP-DEV] [Concept] Flip relative function lookup order (global,
 then local)
To: PHP internals <internals@lists.php.net>
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From: tovilo.ilija@gmail.com (Ilija Tovilo)

Hi Levi

On Tue, Aug 20, 2024 at 5:14=E2=80=AFPM Levi Morrison
<levi.morrison@datadoghq.com> wrote:
>
> I have long been in favor of a larger BC break with better language
> consistency. Class lookup and function lookup with respect to
> namespaces should be treated the same. The difficulty is getting a
> majority of people to vote yes for this. Keep in mind that qualifying
> every global function is annoying but probably can be somewhat
> automated, and will bring better performance. So again, this improves
> the existing code even without upgrading.
>
> Yes, there would be complaints about it. Yes, there are probably some
> people or projects who wouldn't upgrade. I don't particularly care, as
> there are increasingly more operating systems and companies providing
> LTS support for long periods of time. Probably Zend.com will offer LTS
> support for the last PHP 8.X release, and possibly there will be some
> distro which also has it. I believe it's the right thing to do
> because:
>
>  1. It's faster.
>  2. It enables function autoloading in a similar manner to class autoload=
ing.
>  3. It's more consistent, and simpler to teach and maintain.
>
> It's rare that you get all of these together, often you have to make
> tradeoffs within them.

The approach I originally proposed also solves 1. and 2. (mostly) with
very little backwards incompatibility. Consistency is absolutely
something to strive for, but not at the cost of breaking most PHP
code.

To clarify on 2.: The main issue with function autoloading today is
that the engine needs to trigger the autoloader for every unqualified
call to global functions, given that the autoloader might declare the
function in local scope. As most unqualified calls are global calls,
this adds a huge amount of overhead.

Gina solved this in part by aliasing the local function to the global
one after the first lookup. However, that still means that the
autoloader will trigger for every new namespace the function is called
in, and will also pollute the function table.

Reversing the lookup order once again avoids local lookup when calling
global functions in local scope, which also means dodging the
autoloader. The caveat is that calling local functions in local scope
triggers the autoloader on first encounter, but at least it can be
marked as undeclared in the symbol table once, instead of in every
namespace, which also means triggering the autoloader only once.

Ilija