Description:
------------
So, this is not really a bug itself but it's a problem.
Let's say we have:

class a {
  var $a = array('a'=>1);
[...] some functions [...]
};

Lets say a function inside the class does:
var_dump($this->a); //this will dump $a array of class a.
If we do var_dump($this->a['a']) it will dump integer 1.
If we do:
$z="a"; var_dump($this->$z); it will dump $a array of class a.
Since here all is working fine because $z is used as a pointer.
What happens with?
$z="a"; var_dump($this->$z['a']);
So, this will again dump the $a array in the class.

The problem here is the following, because of the operator precedence, the index ['a'] is considered an index of $z which is a string. Then 'a' is casted to integer and interpreted as 0.
$this->$z['a'] becomes the same as $this->$z[0] and, as $z[0] is 'a', this becomes $this->a (the array).

This is not really a problem (even its not clear this precedence in the documentation as posted in other bug).
My problem is that I couldn't find any way of telling the php interpreter that ['a'] should be considered as an index for the whole expression.

($this->$a)['a'] gives syntax error and I have been trying to find a way to do this without intermediate variables and couldn't figure out a solution.

I know this example has no sense (who would really do this?) but still think there should be a way to specify the precedence (and if there is, it should be documentated in the operator precedence page, which lacks of the -> operator by the way).

Thanks,
Diego