[VOTE] [RFC] Anonymous Classes

On Fri, Mar 13, 2015 at 8:33 PM, Philip Sturgeon pjsturgeon@gmail.com
wrote:

A two week discussion period has been held and there are no outstanding
issues.

Serialization has been disabled, and generated names have been
explained better in the newest version of the RFC

https://wiki.php.net/rfc/anonymous_classes

The implementation needs to be updated with changes from master, but
that can be done at a later point and should not be used as a reason
to vote against.

I'm not yet sure which way to vote on this RFC. I don't think there's
anything principally wrong with anonymous classes, but the current RFC seems
incomplete to me with regard to scoping (and as future changes in this area
are not necessarily backwards-compatible, I'd rather solve this now than
later). Lets start off with an example from the RFC:

class Outside {
protected $data;

public function __construct($data) {
    $this->data = $data;
}

public function getArrayAccess() {
    return new class($this->data) extends Outside implements ArrayAccess

{
public function offsetGet($offset) { return
$this->data[$offset]; }
public function offsetSet($offset, $data) { return
($this->data[$offset] = $data); }
public function offsetUnset($offset) {
unset($this->data[$offset]); }
public function offsetExists($offset) { return
isset($this->data[$offset]); }
};
}
}

So ... WTF. It probably took me 10 minutes yesterday to finally understand
the evil, evil things this code is doing and why it is doing them. This is
what happens: The new anon class extends Outside (the wrapping class) and as
such also inherits the parent constructor. The new class($this->data) bit
passes $this->data to the constructor (the one inherited from Outside), as
such $this->data will be assigned in the inner class as well. Because the
anonymous class extended from Outside it is allowed to access the protected
$data member.

Why is this (imho very weird and unintuitive) approach used? Quoting from
the RFC: "[E]xtending Outer [sic] allows the nested class implementing
ArrayAccess permission to execute protected methods, declared in the Outer
[sic] class, on the same $this→data".

So the reason behind this is that anonymous classes as implemented by this
RFC - and much unlike the anonymous class implementations you will find in
other languages like Java or D - are considered to be totally unrelated to
the wrapping class and have only "public" access to its scope. I don't think
this is good. The solution ("extends Outside") to work around this that is
presented in the RFC has a number of problems:

• As PHP does not support multiple inheritance, extending Outside for scope
  access means no other class may be extended.
• Extending the wrapping doesn't just give you access to restricted
  methods/properties of the wrapping class - it will also import everything
  into the inner class. This means that the anonymous class will have a bunch
  of additional methods and properties (potentially public ones) which have
  nothing to do with whatever the class is actually for.
• The approach used to pass the data into the inner class by using the
  constructor of the wrapping class assumes that the constructor a) only
  performs simple assignments and b) accepts the entire state of the wrapping
  class as parameters - if this is not the case you will likely not be able to
  duplicate the state of the wrapping class in the inner anonymous class.

To solve this without such hacks, two things are necessary:

a) Assuming that the anonymous class somehow got hold of an instance of the
wrapping class (i.e. it has an object $obj instanceof Outside), it should be
able to access private and protected properties and methods of that object.
This is consistent with the general rule that any code within a class body
can access it's privates, unless explicitly rebound. For example, the
following code should work:

class Outside {
    private $private;
    public function getAnon() {
        return new class($this) {
            private $outside;
            public function __construct($outside) { $this->outside =

$outside; }
public function getPrivateOfOutside() { return
$this->outside->private; }
};
}
}

b) Providing some easy way to access the instance of the wrapping class. The
previous example passed it in as a constructor, which is somewhat verbose. A
possible syntax for accessing the wrapping instance would be Outside::$this
(to borrow Java syntax):

class Outside {
    private $private;
    public function getAnon() {
        return new class {
            public function getPrivateOfOutside() { return

Outside::$this->private; }
};
}
}

Point a) is the more fundamental issue, which I think should be addressed
from the start. It's also not backwards compatible to introduce it as a
later point. Point b) is pretty much just syntax sugar once a) stands. (The
example of a) can be further simplified by using a trait that automatically
implements that constructor and property, to avoid the boilerplate.)

Nikita

I really dont know how I missed this email, but I'm glad we talked
about this elsewhere.

For anyone else concerned, an anon class inside a parent class is only
able to act with its public interface. Yes, that is weird, but there
is currently no support in PHP for nested classes.

This is what Nikita wants:

http://3v4l.org/QLFoJ/rfc#rfc-anonymous_classes

Right now that gives:

Fatal error: Cannot access private property Outside::$private in

/in/QLFoJ on line 12

Joe plans to bring back Nested Classes
(https://wiki.php.net/rfc/nested_classes) and when that is done -
hopefully for 7.1 - this code will start to work. Doing things this
way is perfectly BC because it currently fatal errors and in the
future will actually work.

So, this should be all good. It's sad we don't have all of everything
right now, but this is a good step on the way. :)