Object to Array conversion tests

[Ocramius]

This PR simply introduces two tests to prevent unwanted BC breaks in how objects are converted to arrays.

This (as far as I know) happens in two cases:

• When explicitly calling $data = (array) $object;
• When using __sleep

This PR simply adds tests that verify the keys of the arrays being generated.

[nikic]

This seems more like a behavior we should fix rather than test. (array) $object should return the public properties only (similarly to what happens when iterating over the object with foreach).

[Ocramius]

@nikic I'm actually gaining huge performance improvements from this by avoiding reflection. If this is unexpected behavior, then an alternate solution that gives me an array copy of an object could be required.

This representation actually makes a lot of sense to me, since it allows me to get data for larger hierarchies too:

class Foo
{
    private $bar;
}

class Bar extends Foo
{
    private $bar;
}

class Baz extends Bar
{
    private $bar;
}

var_dump((array) new Baz()); // gives me 3 keys - awesome!

Via reflection, I have to re-build all this myself, resulting in quite a mess, especially given the ORM performance requirements. I actually think it's a really nice feature.

[Ocramius]

Recap after discussion on http://chat.stackoverflow.com/transcript/message/10116460#10116460 :

• This PR is not about "freezing" the feature
• This PR aims at providing documentation for the feature, so that eventual BC breaks explicitly show up in a committers' build
• I have no problems with the API changing in future, but I'd gladly see a bulk "write-" and "read-" non-public fields API that allows me to break OO rules as I'm doing here (for a good reason) without using reflection (because of the performance implications)

/cc @jpauli

[smalyshev]

I'm not a big fan of exposing internal implementation, but I guess there's no harm in making any further change in this area explicit.

[php-pulls]

Comment on behalf of stas at php.net:

merged