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/
