array_only_keys() and array_except_keys()

The RFC targeted PHP 8.6 and needed a two-thirds majority. It was declined 2 to 9, with 9 abstaining, when voting closed on March 26, 2026.

Keeping some keys of an array, or dropping a few, is a common task, and many frameworks ship helpers for it, like Laravel's Arr::only() and Arr::except(). This RFC from Muhammed Arshid KV proposed two native functions to do the same job in PHP: array_only_keys() and array_except_keys(). It was declined.

How it would have worked#

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

The first function keeps only the keys you list, and the second keeps everything except the keys you list.

$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]

The RFC set out a few rules:

• Both functions return a new array and leave the original unchanged.
• Keys keep their original order.
• Keys that don't exist are skipped without an error.
• Duplicate keys in $keys are ignored.
• Both string and integer keys work.

Why add them#

You can already write these in userland:

function array_only_keys(array $input, array $keys): array {
    return array_intersect_key($input, array_flip($keys));
}

That works, but array_flip() builds an extra array in memory first. The RFC argues that a native C version can skip that step and copy values straight into the result, which uses less memory, especially with large key lists or inside loops.

What it means for existing code#

According to the RFC, nothing breaks. It only adds two new functions to the standard library.