init一个成员变量与null之间的区别是什么？ [重复]

Example A:

class F {
  private $f = null;
}

Example B:

class F {
  private $f;
}

Any different between those two classes?

</div>

There is no difference between these two variable both of consider as null

-------------------------------------------------------------------------------
|   Expression     | gettype()  | empty()  | is_null()  | isset()  | boolean  |
-------------------------------------------------------------------------------
| $f = null;       | NULL       | TRUE     | TRUE       | FALSE    | FALSE    |
| $f;              | NULL       | TRUE     | TRUE       | FALSE    | FALSE    |
-------------------------------------------------------------------------------

This is from @RexM answers

null is a special placeholder value in the programming language that literally means "nothing". It's not 0, it's not an empty string, it's nothing. There is no value in memory being pointed to. An empty string, on the other hand, is still a string object, just a very short one :)