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Date: Thu, 16 Mar 2017 15:01:55 +0100
Message-ID: <CADyq6sKjSfWXuUp3tehmjLQ-cEVRD7qQZhCSrDyn64f9pD96yw@mail.gmail.com>
To: Andrey Andreev <narf@devilix.net>
Cc: Ryan Pallas <derokorian@gmail.com>, PHP Internals List <internals@lists.php.net>, 
	=?UTF-8?Q?Beno=C3=AEt_Burnichon?= <bburnichon@gmail.com>, 
	Kalle Sommer Nielsen <kalle@php.net>
Content-Type: multipart/alternative; boundary=001a114787a6325df5054ad9825f
Subject: Re: [PHP-DEV] Add __toArray() method to objects that would be called
 on cast to array
From: ocramius@gmail.com (Marco Pivetta)

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Content-Type: text/plain; charset=UTF-8

Since some folks keep banging on "it's not a BC break", I propose a
challenge in fixing this particular BC break example (reads: find a
different way to make it work, and no warnings/notices allowed):

I made a very simplistic example of where `__toArray` will break existing
API that currently literally accepts any kind of object:
https://3v4l.org/Tj0GH

For reference, here's the code copy:

<?php

class Foo
{
    public $bar;
    public $baz;
    public $taz;
}

// please note that this API has a signature of `object $object` - any
object allowed.
function unsetProperties($object) {
    // we ignore inheritance and private properties for simplicity
    return array_diff(
        array_map(
            function (\ReflectionProperty $p) : string {
                return $p->getName();
            },
            (new ReflectionClass($object))->getProperties()
        ),
        array_keys((array) $object)
    );
}

var_dump(unsetProperties(new Foo));

$foo = new Foo;

unset($foo->baz);

var_dump(unsetProperties($foo));

There are dozens of simpler examples that break (typically, data-mapper
layers): I picked this particular one because there is no other way to
detect unset properties without causing side-effects.

If `__toArray` is implemented on an object, the API defined above will
either report all properties to be unset, or in general produce unreliable
results.

The current API specification of the `(array)` operator is as following:

 * for every SET property produce an array value, with the key being:
    * "\0" . $className . "\0" . $propertyName for private properties
    * "\0*\0" . $propertyName for protected properties
    * $propertyName for public properties
    * $propertyName for dynamically defined properties

This is a **VERY SPECIFIC** behavior that the operator currently
guarantees. Break that, and you can go on github hunting for `(array)` cast
usages.

The behavior was frozen in the current suite in https://github.com/php/php-
src/blob/8015daeddb7bb4951c808fa253b97753787fb0ea/tests/classes/
array_conversion_keys.phpt (although, now that I notice, doesn't cover
dynamically defined properties - should add that).

Marco Pivetta

http://twitter.com/Ocramius

http://ocramius.github.com/

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