Hi,
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.
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.
On Sun, 22 Feb 2026, 11:55 pm Tim Düsterhus, <[email protected]> wrote:
> Hi
>
> The same comments as with your other RFC apply here.
>
> On 2/20/26 18:37, Muhammed Arshid KV wrote:
> > 1. 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”?
>
> > 2. 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
>
