PHP RFC: array_only_keys() and array_except_keys()
- Version: 1.2
- Date: 2026-02-20
- Author: Muhammed Arshid KV, arshidkv12@gmail.com
- Status: Declined
- 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 $data = [ 'id' => 1, 'name' => 'Name here', 'email' => 'name@test.com', ]; array_only_keys($data, ['id', 'email']); // Output // ['id' => 1, 'email' => 'name@test.com'] array_except_keys($data, ['email']); // Output // ['id' => 1, 'name' => 'Ali'] ?>
Here is a simple example of an array_only_keys() and array_except_keys implementation using existing PHP functions:
<?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($keys)); }
This works, but array_flip($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.
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 array_only_keys([], ['a']); // [] array_except_keys([], ['a']); // [] array_only_keys(['a'=>1], []); // [] array_except_keys(['a'=>1], []); // ['a'=>1] ?>
Non-Existing Keys
<?php array_only_keys(['a'=>1], ['b']); // [] array_except_keys(['a'=>1], ['b']); // ['a'=>1] ?>
Numeric Keys
<?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] ?>
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:
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
