Temp data that must be destroyed at end of lifecycle

@Dave friend: Thanks for your answer

I have an abstract class User
Maybe, the best solution is to have a public static property in this class : $current_user
and then, I can access like this:
User::$current_user

Yes, that would work. Any data that is held only in (non-persistent) memory like a class instance object will automatically be destroyed when script execution ends. I assumed from the original question that you were using something that was potentially persistent like session data or a temp database table.