Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:130209
Precedence: list
MIME-Version: 1.0
Date: Sun, 01 Mar 2026 15:10:36 +0100
To: Muhammed Arshid KV <arshidkv12@gmail.com>
Cc: Claude Pache <claude.pache@gmail.com>, internals@lists.php.net
Subject: =?UTF-8?Q?Re=3A_=5BPHP-DEV=5D_=5BRFC=5D_array=5Fonly=28=29_and_a?=
 =?UTF-8?Q?rray=5Fexcept=28=29_=E2=80=93_Utility_functions_for_array_key_f?=
 =?UTF-8?Q?iltering?=
In-Reply-To: <CAO3bawnw7WvNT=1PDa0rw+S5_5aKnM6kYSOdL=zY8kpXwtV6eQ@mail.gmail.com>
References: <CAO3baw=Qe-w4UOQzc4_NO=b41N-DJtf8U9Q6HybMCcCtZoEqgA@mail.gmail.com>
 <3ACF2D3E-0376-4033-8CAA-84FAD83E2A69@gmail.com>
 <CAO3baw=A5hnGCWbY3_4LE=nYm8+=R1kcAvfjKQWLS-ODyXx0Kw@mail.gmail.com>
 <f0891adc-f114-4217-9ac9-1692d8226f8c@bastelstu.be>
 <CAO3bawnw7WvNT=1PDa0rw+S5_5aKnM6kYSOdL=zY8kpXwtV6eQ@mail.gmail.com>
Message-ID: <359310a0d41524f9d7187e75379b16a9@bastelstu.be>
Content-Type: text/plain; charset=UTF-8;
 format=flowed
Content-Transfer-Encoding: 8bit
From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

Am 2026-02-22 19:58, schrieb Muhammed Arshid KV:
> Here is a simple example of an `array_only()` implementation using 
> existing
> PHP functions:
> 
> ```php
> function array_only(array $input, array $keys): array {
>     return array_intersect_key($input, array_flip($keys));
> }
> ```
> 
> This works, but `array_flip($keys)` creates an extra temporary hash 
> table.
> So peak memory becomes: input + keys + flipped array + result.

That is true for this specific implementation of a “wrapper function”. 
It is not necessarily true for other implementations, e.g. simply using 
the functions directly instead of creating a wrapper for two method 
calls. `array_flip()` supports compile-time evaluation, so you can just 
write:

     $dataWithOnlyIdAndEmail = \array_intersect_key($data, 
\array_flip(['id', 'email']));

and OPcache will make sure to rewrite it to:

     $dataWithOnlyIdAndEmail = \array_intersect_key($data, ['id' => 0, 
'email' => 1]);

avoiding the intermediate array.

Best regards
Tim Düsterhus

PS: It appears that the RFC is not listed in the overview at 
https://wiki.php.net/rfc.