[PHP-DEV] Pre-RFC discussion about adding friendship to PHP

Mailing Lists php.internals
1

Hi internals,

I’d like to add support for friendship in PHP. I don’t mean friendship in the PSR-8 huggable way, but rather in the C++ way of allowing access to non-public parts of a class without needing to use Reflection.

I haven’t started work on implementing this yet, but there is a big question about how to indicate friendship that I wanted to get some feedback on. Specifically, should it be added with a new keyword, or with an attribute?

Keyword

  • matches C++
  • suggests that friends are aspects of the class, like properties and constants and methods
  • but would look a bit ugly if we added support for friends that are just for specific properties/methods/constants

Attribute

  • matches how other metadata is added to classes
  • would make it look cleaner if subsequently support was added for friendship being applied to specific properties/methods/constants
  • would differ from the current builtin attributes in that it doesn’t just add/remove warnings, but changes some functionality

For a more in-depth explanation of the inspiration and these two potential approaches, see https://scherzer.dev/Blog/20260309-php-friends. To be clear, I have not yet written an implementation, much less the RFC, but I wanted to get some initial feedback on if people would prefer a new keyword, or an attribute, for declaring friends.

-Daniel

2

Hi

Am 2026-04-29 19:30, schrieb Daniel Scherzer:

I haven't started work on implementing this yet, but there is a big
question about how to indicate friendship that I wanted to get some
feedback on. Specifically, should it be added with a new keyword, or with
an attribute?

It should be a proper keyword for the reasons that are also mentioned in your blog post: Attributes are not part of the public API and thus do not contribute to e.g. LSP checks. They are also expected to gracefully degrade when they do not exist, which means that running code written with friendship in mind on older PHP versions will silently expose a different API instead of failing in a visible way.

See also the reasoning that I provided in the #[\Override] RFC: PHP: rfc:marking_overriden_methods. I think the related mailing list discussion provides additional context - and I seem to remember I wrote something similar in some other RFC discussion as well.

Best regards
Tim Düsterhus

3

On Wed, Apr 29, 2026, at 19:30, Daniel Scherzer wrote:

Hi internals,

I’d like to add support for friendship in PHP. I don’t mean friendship in the PSR-8 huggable way, but rather in the C++ way of allowing access to non-public parts of a class without needing to use Reflection.

I haven’t started work on implementing this yet, but there is a big question about how to indicate friendship that I wanted to get some feedback on. Specifically, should it be added with a new keyword, or with an attribute?

Keyword

  • matches C++
  • suggests that friends are aspects of the class, like properties and constants and methods
  • but would look a bit ugly if we added support for friends that are just for specific properties/methods/constants

Attribute

  • matches how other metadata is added to classes
  • would make it look cleaner if subsequently support was added for friendship being applied to specific properties/methods/constants
  • would differ from the current builtin attributes in that it doesn’t just add/remove warnings, but changes some functionality

For a more in-depth explanation of the inspiration and these two potential approaches, see https://scherzer.dev/Blog/20260309-php-friends. To be clear, I have not yet written an implementation, much less the RFC, but I wanted to get some initial feedback on if people would prefer a new keyword, or an attribute, for declaring friends.

-Daniel

Hi Daniel,

We saw some friendship discussions in my nested class RFC, where nested classes implicitly became friends of the outer class. I’d recommend checking those threads for feedback about friendship and scope.

— Rob

4

On Wed, Apr 29, 2026, at 12:30 PM, Daniel Scherzer wrote:

Hi internals,

I'd like to add support for friendship in PHP. I don't mean friendship
in the PSR-8 huggable way,

Aw, but why not?

but rather in the C++ way of allowing access
to non-public parts of a class without needing to use Reflection.

I haven't started work on implementing this yet, but there is a big
question about how to indicate friendship that I wanted to get some
feedback on. Specifically, should it be added with a new keyword, or
with an attribute?

Keyword
* matches C++
* suggests that friends are aspects of the class, like properties and
constants and methods
* but would look a bit ugly if we added support for friends that are
just for specific properties/methods/constants

Attribute
* matches how other metadata is added to classes
* would make it look cleaner if subsequently support was added for
friendship being applied to specific properties/methods/constants
* would differ from the current builtin attributes in that it doesn't
just add/remove warnings, but changes some functionality

For a more in-depth explanation of the inspiration and these two
potential approaches, see
Blog: Friends in PHP. To be clear, I have not
yet written an implementation, much less the RFC, but I wanted to get
some initial feedback on if people would prefer a new keyword, or an
attribute, for declaring friends.

-Daniel

There was a lot of related discussion around module/package/file visibility not too long ago that is also worth reviewing. Currently I am highly skeptical of friend classes, as I believe module-level visibility is more useful than class-level, in general.

That said, were we to go this route, I agree that keywords would be the way to go for the reasons given in the blog post. Also, there's some plumbing already i place via aviz, at least for properties. In concept, the following should be possible:

class User {
  friend UserFactory;

  public friend(set) string $name;
}

class UserFactory {
  public function makeUser($name) {
    $u = new User();
    $u->name = $name; // This is OK, because UserFactory is a friend.
    return $u;
  }
}

$factory = new UserFactory();
$u = $factory->makeUser('Larry');

print $u->name; // OK, because public get
$u->name = 'Daniel'; // Error, because not a friend.

Whether that makes sense to extend to methods, I don't know.

--Larry Garfield

5

On Mon, May 4, 2026 at 12:50 PM Larry Garfield <larry@garfieldtech.com> wrote:

On Wed, Apr 29, 2026, at 12:30 PM, Daniel Scherzer wrote:

Hi internals,

I’d like to add support for friendship in PHP.

-Daniel

There was a lot of related discussion around module/package/file visibility not too long ago that is also worth reviewing. Currently I am highly skeptical of friend classes, as I believe module-level visibility is more useful than class-level, in general.

I think that perfect should not be the enemy of good, and this also lays the groundwork for namespace-level friends in the future. We shouldn’t wait for a potential future “module-level visibility” if we can have friends now.

That said, were we to go this route, I agree that keywords would be the way to go for the reasons given in the blog post. Also, there’s some plumbing already i place via aviz, at least for properties. In concept, the following should be possible:

class User {
friend UserFactory;

public friend(set) string $name;
}

I think having friends that can access everything is more helpful than a new level of visibility - if you declare a class as a friend you already know that the class exists and wants to access private implementation details, so you can trust it to upload the class invariants.

-Daniel