private variables and inheritance

david8787

I came across a test question that says given this class, extend it so you have functions to get and set the private variables. It goes on to say that there are multiple ways to do this.

class myClass {

  private $myVar1 = 1;
  private $myVar2 = 2;
  private $myVar3 = 3;

  public function output() {
    print ($this->myVar1+$this->myVar2+$this->myVar3);
  }

}

From my understanding this is not possible unless the variables are protected. Am I missing something, or am I not fully understanding OOP in PHP?

laserlight

It should not be possible. If it is, then it may be a bug with the PHP interpreter, or possibly PHP itself (unless it requires some esoteric hack that should result in its perpetrator being exposed on thedailywtf and then fired).

NogDog

I wonder if they used the word "extend" incorrectly, or at least confusingly? For instance, if you took it to mean "enhancing" that class by using set() and get() methods, that could be done. But one would hope that anyone creating such a question would not use such confusing terminology. :rolleyes:

halojoy

When a class extends another parent class
he can only use public and protected variables and functions
from the parent class..
So, you are right. private means private!

If we run this case, the displayed result will be: 1
... and with 2 notices:
Undefined property: theshow::$myVar2
Undefined property: theshow::$myVar3

But the new class also will have access to a public function output()
and by using this function he can access those private variables.
If we run $var->output, the displayed result will be: 6

<?php

class myClass {

  protected $myVar1 = 1;
  private   $myVar2 = 2;
  private   $myVar3 = 3;

  public function output() {
    print ($this->myVar1+$this->myVar2+$this->myVar3);
  }

}

class theshow extends myClass {

  public function show() {
    print ($this->myVar1+$this->myVar2+$this->myVar3);
  }

}

$var = new theshow();

$var->show();  // result: 1

$var->output();  // result: 6
?>