====== PHP RFC: array_only_keys() and array_except_keys() ======
  * Version: 1.2
  * Date: 2026-02-20 
  * Author: Muhammed Arshid KV, arshidkv12@gmail.com
  * Status: Voting
  * Implementation: TBD


===== Introduction =====
Working with arrays often requires selecting or excluding a subset of keys. Many frameworks provide helper functions like array_only_keys() and array_except_keys() because developers repeatedly re‑implement this logic. This RFC proposes adding native PHP functions for these common operations.

    * function array_only_keys(array $array, array $keys): array {}
    * function array_except_keys(array $array, array $keys): array {}

===== Proposal =====
Add two new functions to the PHP core: 

The usage of the methods to handle the keys will look like:

<PHP>
<?php
$data = [
    'id' => 1,
    'name' => 'Name here',
    'email' => 'name@test.com',
];

array_only_keys($data, ['id', 'email']);
// Output
// ['id' => 1, 'email' => 'name@test.com']

array_except_keys($data, ['email']);

// Output
// ['id' => 1, 'name' => 'Ali']

?>
</PHP>

Here is a simple example of an array_only_keys() and array_except_keys implementation using existing PHP functions:
<PHP>
<?php
function array_only_keys(array $input, array $keys): array {
    return array_intersect_key($input, array_flip($keys));
}
function array_except_keys(array $array, array $keys) {
    return array_diff_key($array, array_flip($keys));
}
</PHP>

This works, but <php>array_flip($keys)</php> creates an extra temporary hash table.
So peak memory becomes: input + keys + flipped array + result.

In a native C implementation, we can iterate over <php>$keys</php> 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.

See the implementation in Laravel:
https://github.com/laravel/framework/blob/12.x/src/Illuminate/Collections/Arr.php#L724-L727

Laravel Arr::except implementation:
https://github.com/laravel/framework/blob/12.x/src/Illuminate/Collections/Arr.php#L231-L236

==== Detailed Behavior ====

  - The functions return a new array.
  - The original array remains unchanged.
  - The original key order is preserved.
  - Missing keys are ignored silently.
  - Duplicate keys in $keys are ignored.
  - Works with both associative and numeric arrays.

==== Empty Input Conditions ====
<PHP>
<?php
array_only_keys([], ['a']);        // []
array_except_keys([], ['a']);      // []

array_only_keys(['a'=>1], []);     // []
array_except_keys(['a'=>1], []);   // ['a'=>1]
?>
</PHP>

==== Non-Existing Keys ====

<PHP>
<?php

array_only_keys(['a'=>1], ['b']);      // []
array_except_keys(['a'=>1], ['b']);    // ['a'=>1]
?>
</PHP>
==== Numeric Keys ====
<PHP>
<?php
$a = [10, 20, 30, 40];

array_only_keys($a, [1, 3]);
// [1 => 20, 3 => 40]

array_except_keys($a, [0, 2]);
// [1 => 20, 3 => 40]
?>
</PHP>
===== Backward Incompatible Changes =====
None
 
===== Proposed PHP Version(s) =====
PHP 8.6

===== RFC Impact =====
==== To Existing Extensions ====

These two new functions are added to ext-standard, where array_only_keys() and array_except_keys() and array_only_keys() and array_except_keys() also live.
 

===== Voting Choices =====

Primary Vote requiring a 2/3 majority to accept the RFC:

<doodle title="Add array_only_keys() and array_except_keys()" voteType="single" closed="false" closeon="2026-03-26T15:30:00Z">
   * Yes
   * No
   * Abstain
</doodle>

===== Patches and Tests =====
None

===== References =====
Current discussion: https://externals.io/message/130102

===== Rejected Features =====
None

===== Changelog =====

1.0: Initial version under discussion

1.1 Changed function names array_only() and array_except()

1.2 Laravel's link added