[RFC] array_only() and array_except() – Utility functions for array key filtering

1 month ago by Muhammed Arshid KV — view source — reply

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Hello Internals,

I would like to propose a new RFC titled array_only() and array_except().

RFC: https://wiki.php.net/rfc/array_only_except
https://wiki.php.net/rfc/array_only_except?utm_source=chatgpt.com

This RFC proposes adding two utility functions to the PHP core:

• array_only(array $array, array $keys): array
• array_except(array $array, array $keys): array

These functions allow selecting or excluding specific keys from an array.

Similar helpers are commonly used in frameworks, and adding native support
would improve readability and consistency in userland code.

Summary:

• array_only() returns a new array containing only the specified keys.
• array_except() returns a new array excluding the specified keys.
• Original array is not modified.
• Works with associative and numeric keys.
• No impact on SAPIs or on OPcache.

I would appreciate feedback and suggestions from the community.
If there is general agreement, I plan to move the RFC forward.

Thanks,
Muhammed Arshid KV

1 month ago by Claude Pache — view source — reply

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Le 20 févr. 2026 à 10:25, Muhammed Arshid KV arshidkv12@gmail.com a écrit :

Hello Internals,

I would like to propose a new RFC titled array_only() and array_except().

RFC: https://wiki.php.net/rfc/array_only_except https://wiki.php.net/rfc/array_only_except?utm_source=chatgpt.com
This RFC proposes adding two utility functions to the PHP core:

• array_only(array $array, array $keys): array
• array_except(array $array, array $keys): array

These functions allow selecting or excluding specific keys from an array.

Similar helpers are commonly used in frameworks, and adding native support would improve readability and consistency in userland code.

Summary:

• array_only() returns a new array containing only the specified keys.
• array_except() returns a new array excluding the specified keys.
• Original array is not modified.
• Works with associative and numeric keys.
• No impact on SAPIs or on OPcache.

I would appreciate feedback and suggestions from the community.
If there is general agreement, I plan to move the RFC forward.

Thanks,
Muhammed Arshid KV

Hi,

The principle of the RFC is interesting to me, as it is a situation I encounter from time to time. Two remarks:

It may be interesting to compare with currently available solutions. Currently, I use array_intersect_key and array_diff_key when I need the semantics of proposed array_only and array_except:

array_intersect_key($data, ['id' => null, 'email' => null]);

I think that the name of the new functions ought to make evident that we are filtering on keys and not on something else. I suggest: array_only_keys and array_except_keys.

—Claude

1 month ago by mickmackusa — view source — reply

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It seems clear to me that this proposal was under-researched because the
RFC doesn't even acknowledge the fact that PHP already has native functions
which serve the exact same purpose (and they have more indicative names).

I'm not a voter, but I would vote No on this one because the new functions
aren't adding significant value to the language.

Mick

1 month ago by Muhammed Arshid KV — view source — reply

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Hi,

Thanks for the feedback.

Yes, *array_intersect_key() *and *array_diff_key() *can be used today,
but the RFC proposes dedicated functions for better readability, less
boilerplate, and potentially better performance and lower memory usage by
avoiding temporary arrays.
Good point about naming. Making the key-filtering behavior explicit
(e.g., array_only_keys and array_except_keys) improves clarity and
avoids confusion.

Le 20 févr. 2026 à 10:25, Muhammed Arshid KV arshidkv12@gmail.com a
écrit :

Hello Internals,

I would like to propose a new RFC titled array_only() and array_except()
.

RFC: https://wiki.php.net/rfc/array_only_except
https://wiki.php.net/rfc/array_only_except?utm_source=chatgpt.com

This RFC proposes adding two utility functions to the PHP core:

• array_only(array $array, array $keys): array
• array_except(array $array, array $keys): array

These functions allow selecting or excluding specific keys from an array.

Similar helpers are commonly used in frameworks, and adding native support
would improve readability and consistency in userland code.

Summary:

• array_only() returns a new array containing only the specified keys.
• array_except() returns a new array excluding the specified keys.
• Original array is not modified.
• Works with associative and numeric keys.
• No impact on SAPIs or on OPcache.

I would appreciate feedback and suggestions from the community.
If there is general agreement, I plan to move the RFC forward.

Thanks,
Muhammed Arshid KV

Hi,

The principle of the RFC is interesting to me, as it is a situation I
encounter from time to time. Two remarks:

It may be interesting to compare with currently available solutions.
Currently, I use array_intersect_key and array_diff_key when I need
the semantics of proposed array_only and array_except:
array_intersect_key($data, ['id' => null, 'email' => null]);
I think that the name of the new functions ought to make evident that
we are filtering on keys and not on something else. I suggest:
array_only_keys and array_except_keys.

—Claude

1 month ago by tim@bastelstu.be — view source — reply

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The same comments as with your other RFC apply here.

Yes, *array_intersect_key() *and *array_diff_key() *can be used today,
but the RFC proposes dedicated functions for better readability, less
boilerplate, and potentially better performance and lower memory usage by
avoiding temporary arrays.

Can you elaborate on what you mean by “lower memory usage by avoiding
temporary arrays”?

Good point about naming. Making the key-filtering behavior explicit
(e.g., array_only_keys and array_except_keys) improves clarity and
avoids confusion.

I don't think that array_(only|except)_keys() is particularly clear.
From the naming I would expect it to return the array keys / values
(i.e. do the same as array_keys() and array_values() respectively).

Best regards
Tim Düsterhus

1 month ago by Muhammed Arshid KV — view source — reply

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Hi,

Here is a simple example of an array_only() implementation using existing
PHP functions:

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.

In a native C implementation, we can iterate over $keys and copy values
directly into the result without creating that temporary array. That means
fewer allocations and lower peak memory usage, especially with large key
sets or inside loops.

Thanks.

Hi

The same comments as with your other RFC apply here.

Yes, *array_intersect_key() *and *array_diff_key() *can be used today,
but the RFC proposes dedicated functions for better readability, less
boilerplate, and potentially better performance and lower memory usage by
avoiding temporary arrays.

Can you elaborate on what you mean by “lower memory usage by avoiding
temporary arrays”?

Good point about naming. Making the key-filtering behavior explicit
(e.g., array_only_keys and array_except_keys) improves clarity and
avoids confusion.

I don't think that array_(only|except)_keys() is particularly clear.
From the naming I would expect it to return the array keys / values
(i.e. do the same as array_keys() and array_values() respectively).

Best regards
Tim Düsterhus

1 month ago by tim@bastelstu.be — view source — reply

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Am 2026-02-22 19:58, schrieb Muhammed Arshid KV:

Here is a simple example of an array_only() implementation using
existing
PHP functions:
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.

1 month ago by Muhammed Arshid KV — view source — reply

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Hi Tim,

Thanks for the explanation.

In this example,

$dataWithOnlyIdAndEmail = \array_intersect_key($data, ['id' => 0, 'email'
=> 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

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:
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.

1 month ago by Muhammed Arshid KV — view source — reply

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Hi,

I think the RFC “array_only_except” is ready to move to the voting phase.

If there are no further objections or required changes, I would like to
proceed with starting the vote.

Thanks.

1 month ago by Ben Ramsey — view source — reply

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Hi,

I think the RFC “array_only_except” is ready to move to the voting
phase.

If there are no further objections or required changes, I would like
to proceed with starting the vote.

Thanks.

Unless I've missed something, I don't think the RFC has addressed any of
the feedback from the discussion on this list.

Claude Pache suggested:

It may be interesting to compare with currently available solutions.

And Mick suggested something similar:

the RFC doesn't even acknowledge the fact that PHP already has
native functions which serve the exact same purpose

On the list you acknowledged array_intersect_key() and
array_diff_key(), saying:

the RFC proposes dedicated functions for better readability, less
boilerplate, and potentially better performance and lower memory
usage.

I would have expected all of this to be added to the RFC to provide
further rationale for why these new functions are needed, along with
some numbers to back up the better performance and lower memory usage
claims.

In another reply to the list, you seemed to indicate that you were going
to change the names of the functions in the RFC:

Good point about naming. Making the key-filtering behavior explicit
(e.g., array_only_keys and array_except_keys) improves clarity and
avoids confusion.

Did you decide against changing the names in the RFC? I don't see any
updates to that effect.

I'd like to see the feedback addressed within the RFC before opening it
for a vote. It think it would make the RFC stronger.

Cheers,
Ben

30 days ago by Muhammed Arshid KV — view source — reply

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Unless I've missed something, I don't think the RFC has addressed any of
the feedback from the discussion on this list.

Thank you for the feedback and for taking the time to review the RFC.

I have updated the RFC to address the points raised in the discussion.

Please have a look when you have a chance and let me know if anything still
needs improvement.

Regards

Muhammed Arshid

30 days ago by Ben Ramsey — view source — reply

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Hi

Unless I've missed something, I don't think the RFC has addressed any of
the feedback from the discussion on this list.

Thank you for the feedback and for taking the time to review the RFC.

I have updated the RFC to address the points raised in the discussion.

Please have a look when you have a chance and let me know if anything still
needs improvement.

Regards

Muhammed Arshid

Thanks!

One more thing I'd ask to see in the RFC: can you provide examples of
similar functions that are implemented in PHP userland
libraries/frameworks, as well as point to examples in other programming
languages that provide similar functionality? It would be good to have a
basis for comparison with how others are already approaching this problem.

Cheers,
Ben

29 days ago by Muhammed Arshid KV — view source — reply

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Thanks!

One more thing I'd ask to see in the RFC: can you provide examples of
similar functions that are implemented in PHP userland
libraries/frameworks, as well as point to examples in other programming
languages that provide similar functionality? It would be good to have a
basis for comparison with how others are already approaching this problem.

Cheers,
Ben

I’ve added examples from the Laravel PHP framework.

Cheers,
Arshid

28 days ago by Muhammed Arshid KV — view source — reply

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Hi, it appears the RFC “array_only_except” is ready for voting. I’d
appreciate your feedback.

Regards