Should go to the mailinlist :>
---------- Forwarded message ----------
From: Sebastian Krebs <
[email protected]>
Date: 2012/7/13
Subject: Re: [PHP] Bazar behavior w/ private member variables
To: Nathan Nobbe <
[email protected]>
Hi,
Private properties are only accessable from within an object of the class,
where it's defined. If you define a new private property with the same name
in a subclass, then you just have two properties with the same name, but in
different classes. They are separate from each other ;) It seems, that you
are _really_ looking for protected properties instead.
Regards,
Sebastian
2012/7/13 Nathan Nobbe <
[email protected]>
> On Thu, Jul 12, 2012 at 9:23 PM, Nathan Nobbe <
[email protected]
> >wrote:
>
> > On Thu, Jul 12, 2012 at 8:38 PM, Tommy Pham <
[email protected]> wrote:
> >
> >> On Thu, Jul 12, 2012 at 7:19 PM, Nathan Nobbe <
[email protected]>
> >> 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.
> >>
> >
> > I know that sounds like it should make sense but if it's true, it's an
> > aspect I've never known about, at least maybe I'm just spacing really bad
> > or something...
> >
> > Anyway, this chokes in javac:
> >
> > public class PrivateAccess
> > {
> > private Boolean isAccessible = true;
> > }
> >
> > class PrivateAccessChild extends PrivateAccess
> > {
> > public Boolean getAccessible()
> > {
> > return isAccessible;
> > }
> > }
> >
> > PrivateAccessChild.java:5: isAccessible has private access in
> PrivateAccess
> > return isAccessible;
> > ^
> >
> > -nathan
> >
>
> Ahhh, but if I add the private declaration in the subclass it works. Where
> have I been??
>
> -nathan
>