Re: Bazar behavior w/ private member variables

On Thu, Jul 12, 2012 at 7:19 PM, Nathan Nobbe <quickshiftin@gmail.com> wrote: > Hi all, > > Strangely PHP seems to let each class have its own layer of private scope > for member variables. If a subclass defines a member variable of the same > name as one defined in the parent the values are maintained independently > in instances of the child class. > > First off a simple class with a private member variable $_myPrivate, and a > public accessor method which returns its value: > > class A > { > private $_myPrivate = 5; > > public function getMyPrivate() > { > return $this->_myPrivate; > } > } > > > Second, a subclass, that gets weird right away, first we define a private > member variable that already has been defined in the parent class, and give > it a different initial value. To illustrate the behavior we have two > accessor methods, setMyPrivate that uses the $this keyword to get the value > of $_myPrivate, which returns the value of the subclasse's version of the > variable, and getParentsMyPrivate, that calls A::getMyPrivate via the > parent keyword and it returns the value of $_myPrivate as defined in the > base class. > > class B extends A > { > private $_myPrivate = 6; > > public function setMyPrivate() > { > $this->_myPrivate = 6; > } > > public function getMyPrivate() > { > return $this->_myPrivate; > } > > public function getParentsMyPrivate() > { > return parent::getMyPrivate(); > } > } > > > Look at a var_dump of an instance of B: > > object(B)#2 (2) { > ["_myPrivate":"B":private]=> > int(6) > ["_myPrivate":"A":private]=> > int(5) > } > > clearly storage is allocated for two different values. Now I'm sure you > all know that if I were to define a private method in A and try to call it > from B a Fatal error is raised, something on the order of > > PHP Fatal error: Call to private method A::tryToCallMeFromB() from context > 'B' > > so why the special treatment for member variables, is this supposed to be a > feature? > > -nathan That is OOP accross all languages. If you want the child class to modify the variable, then set it to protected. Private is only accessible within that class.