You cannot modify private member variables of a different class (Zend Cert)

[crmpicco]

Hey,

I don't have PHP installed on the machine i'm on when coming up against this question in my Zend Cert study. Can anyone advise?

Q: What are the values of $a in $obj_one and $obj_two when this script is executed?

PHP Code:

<?php
class myClass {
  private $a;

  public function __construct() {
    $this->a = 10;
  }

  public function printValue() {
    print "The Value is: {$this->a}\n";
  }

  public function changeValue($val, $obj = null) {
    if(is_null($obj)) {
      $this->a = $val;
    } else {
      $obj->a = $val;
    }
  }

  public function getValue() {
    return $this->a;
  }
}

$obj_one = new myClass();
$obj_two = new myClass();

$obj_one->changeValue(20, $obj_two);
$obj_two->changeValue($obj_two->getValue(), $obj_one);

$obj_two->printValue();
$obj_one->printValue();

?>

Answers:
10,20
You cannot modify private member variables of a different class
20,20
10,10
20,10

I believe it should be "You cannot modify private member variables of a different class". Any thoughts?

Picco

[Fou-Lu]

No, its 20, 20. Object context doesn't hinder PHP's scope visibility, so either instance can be modified in any scope. See this link for visibility from other objects.
This makes sense though. When two types of objects are known to each other, they should logically know what each other know, regardless of if its public or lesser. A better way of writing it for clarity would be:

PHP Code:

public function changeValue($val, MyClass $obj = null) 


Keyword 'self' can also be used as typehint. This is easier to see since we know that both 'this' and 'obj' are MyClass objects, so eachother should know what the other can do.

[crmpicco]

You're spot on Fou-Lu, just tested it locally and you are 100% correct.

The Value is: 20 The Value is: 20

Thanks for the link too.

BTW: what is your name, I keep calling you Fou-Lu ;-)