On Thu, Jul 12, 2012 at 8:38 PM, Tommy Pham <tommyhp2@xxxxxxxxx> wrote:
> On Thu, Jul 12, 2012 at 7:19 PM, Nathan Nobbe <quickshiftin@xxxxxxxxx>
> 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
