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Date: Sun, 1 Mar 2026 19:52:46 +0530
Message-ID: <CAO3baw=mi=DAMBiv9ELx_8dhM_+XDKfrjm1QCo4Kd=HsbPdk9A@mail.gmail.com>
Subject: =?UTF-8?Q?Re=3A_=5BPHP=2DDEV=5D_=5BRFC=5D_array=5Fonly=28=29_and_array=5Fexcept=28=29_?=
	=?UTF-8?Q?=E2=80=93_Utility_functions_for_array_key_filtering?=
To: =?UTF-8?Q?Tim_D=C3=BCsterhus?= <tim@bastelstu.be>
Cc: Claude Pache <claude.pache@gmail.com>, internals@lists.php.net
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From: arshidkv12@gmail.com (Muhammed Arshid KV)

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Hi Tim,

Thanks for the explanation.

In this example,

$dataWithOnlyIdAndEmail =3D \array_intersect_key($data, ['id' =3D> 0, 'emai=
l'
=3D> 1]);


the second argument is an associative array.

But in my *array_only(array $input, array $keys) *function, *$keys* is
a *numeric
array.* Working with a *numeric array* may be slightly faster than building
an associative array first.


Just wanted to clarify that point.


Best regards,

Muhammed Arshid KV

On Sun, 1 Mar 2026, 7:40=E2=80=AFpm Tim D=C3=BCsterhus, <tim@bastelstu.be> =
wrote:

> 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 =E2=80=9Cwrapper funct=
ion=E2=80=9D.
> 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:
>
>      $dataWithOnlyIdAndEmail =3D \array_intersect_key($data,
> \array_flip(['id', 'email']));
>
> and OPcache will make sure to rewrite it to:
>
>      $dataWithOnlyIdAndEmail =3D \array_intersect_key($data, ['id' =3D> 0=
,
> 'email' =3D> 1]);
>
> avoiding the intermediate array.
>
> Best regards
> Tim D=C3=BCsterhus
>
> PS: It appears that the RFC is not listed in the overview at
> https://wiki.php.net/rfc.
>

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<div dir=3D"auto"><p>Hi Tim,</p>
<p>Thanks for the explanation.</p>
<p>In this example,</p><p>$dataWithOnlyIdAndEmail =3D \array_intersect_key(=
$data, [&#39;id&#39; =3D&gt; 0, &#39;email&#39; =3D&gt; 1]);</p><p><br></p>=
<p>the second argument is an associative array.</p><p>But in my <b>array_on=
ly(array $input, array $keys) </b>function, <b>$keys</b> is a <b>numeric ar=
ray.</b> Working with a <b>numeric array</b> may be slightly faster than bu=
ilding an associative array first.</p><p><br></p><p>Just wanted to clarify =
that point.</p><p><br></p><p>Best regards,</p><p>Muhammed Arshid KV</p></di=
v><br><div class=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr" cla=
ss=3D"gmail_attr">On Sun, 1 Mar 2026, 7:40=E2=80=AFpm Tim D=C3=BCsterhus, &=
lt;<a href=3D"mailto:tim@bastelstu.be">tim@bastelstu.be</a>&gt; wrote:<br><=
/div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-le=
ft:1px #ccc solid;padding-left:1ex">Hi<br>
<br>
Am 2026-02-22 19:58, schrieb Muhammed Arshid KV:<br>
&gt; Here is a simple example of an `array_only()` implementation using <br=
>
&gt; existing<br>
&gt; PHP functions:<br>
&gt; <br>
&gt; ```php<br>
&gt; function array_only(array $input, array $keys): array {<br>
&gt;=C2=A0 =C2=A0 =C2=A0return array_intersect_key($input, array_flip($keys=
));<br>
&gt; }<br>
&gt; ```<br>
&gt; <br>
&gt; This works, but `array_flip($keys)` creates an extra temporary hash <b=
r>
&gt; table.<br>
&gt; So peak memory becomes: input + keys + flipped array + result.<br>
<br>
That is true for this specific implementation of a =E2=80=9Cwrapper functio=
n=E2=80=9D. <br>
It is not necessarily true for other implementations, e.g. simply using <br=
>
the functions directly instead of creating a wrapper for two method <br>
calls. `array_flip()` supports compile-time evaluation, so you can just <br=
>
write:<br>
<br>
=C2=A0 =C2=A0 =C2=A0$dataWithOnlyIdAndEmail =3D \array_intersect_key($data,=
 <br>
\array_flip([&#39;id&#39;, &#39;email&#39;]));<br>
<br>
and OPcache will make sure to rewrite it to:<br>
<br>
=C2=A0 =C2=A0 =C2=A0$dataWithOnlyIdAndEmail =3D \array_intersect_key($data,=
 [&#39;id&#39; =3D&gt; 0, <br>
&#39;email&#39; =3D&gt; 1]);<br>
<br>
avoiding the intermediate array.<br>
<br>
Best regards<br>
Tim D=C3=BCsterhus<br>
<br>
PS: It appears that the RFC is not listed in the overview at <br>
<a href=3D"https://wiki.php.net/rfc" rel=3D"noreferrer noreferrer" target=
=3D"_blank">https://wiki.php.net/rfc</a>.<br>
</blockquote></div>

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