PHP Sibling Class Inheritance - php

Question

I'm a bit confused on whether or not this is possible. I've checked a couple of posts here on SO and they don't really explain what I'm looking for.
I have 3 classes. One main class and two classes extending that main class. (see code below). Is it possible to run a method in one of the two extended classes from it's sibling (the other extended class)?
If it's not possible, how can I change my code to accomplish what I'm doing in the example below?
DECLARATION
class A {
public function __construct() {
//do stuff
}
}
class B extends A {
private $classb = array();
public function __construct() {
parent::__construct();
//do stuff
}
public function get($i) {
return $this->classb[$i];
}
public function set($i, $v) {
$this->classb[$i] = $v;
}
}
class C extends A {
public function __construct() {
parent::__construct();
//do stuff
}
public function display_stuff($i) {
echo $this->get($i); //doesn't work
echo parent::get($i); //doesn't work
}
}
USAGE
$b = new B();
$c = new C();
$b->set('stuff', 'somestufftodisplay');
$c->display_stuff('stuff'); // <----- Displays nothing.

Answer 1

Your code shows an additional problem apart from the main question so there are really two answers:
No, you cannot run a method from a sibling class in another sibling class. If you need that, the method should be in the parent class. The same applies to properties.
You cannot use the value of a property from one object in another object, even if they are both of the same class. Setting a property value in one object sets its value only there as different objects can have the same properties with completely different values. If you need to share the value of a property between the objects and also be able to modify it, you should use a static property. In this case you would have to define that in the parent class, see my previous point.
So to make it work, you would need something like
class A {
private static $var = array();
public function get($i) {
return self::$var[$i];
}
public function set($i, $v) {
self::$var[$i] = $v;
}
}
class B extends A {
}
class C extends A {
public function display_stuff($i) {
echo $this->get($i); // works!
}
}
$b = new B();
$c = new C();
$b->set('stuff', 'somestufftodisplay');
$c->display_stuff('stuff');
An example.