Is there some equivalent of \"friend\" or \"internal\" in php? If not, is there any pattern to follow to achieve this behavior?
Edit: Sorry, but st
It is also possible to elevate privileges, aka leaking data selectively, using a handshake and closures in php >=5.3.3.
Basically, the interaction goes: class A has a public method which accepts a class B object, and calls B->grantAccess (or whatever your interface defines), passing it a closure. The closure use($that,$anythingelseyouneed) where $that=$this, and anything else you need to determine what properties are allowed to be accessed. The closure has one argument - the property to return; if it is a property on $that and everything is cool, the closure returns the property. Otherwise, it returns '', or throws an exception, or maybe a default value.
Class B->grantAccess accepts a callable and stores it, using it in other methods to pluck out private properties the closure allows to be leaked. Make class B's default constructor private. Construct a B using a static factory method that takes a Class A argument, to ensure the handshake happens.
Gist here: https://gist.github.com/mcamiano/00592fb400e5043d8acd