PHP Scope and Class Instance Interaction

Question

It seems as though different instances of a class can know about each others' private member variables.

I have provided some code that attempts to showcase my issue, and I will try to explain it.

We have a class with a private member variable, $hidden. modifyPrivateMember sets the value of $hidden to 3. accessPrivateMember takes an Object as a parameter and accesses its private $hidden member to return its value.

Example code:

<?php
// example.php

class Object {
    private $hidden;

    public function modifyPrivateMember() {
        $this->hidden = 3;
    }

    public function accessPrivateMember(Object $otherObject) {
        return $otherObject->hidden;
    }
}

$firstObject = new Object;
$firstObject->modifyPrivateMember();


$otherObject = new Object;
echo $otherObject->accessPrivateMember($firstObject);

Output of the above code:

$ php example.php
3

Can anyone explain why private members of objects are accessible to other instances of the same class? Is there some justification for this ostensible breach of scope?

Answer 1

private means it's restricted to only that class, not only that object.