How can a PHP class that extends another inherit a private function?

Question

I am trying to extend a PHP class without rewriting the whole thing. Here is an example:

<?
$a = new foo();
print $a->xxx();
$b = new bar();
print $b->xxx();

class foo {
  const something = 10;

  public function xxx() {
    $this->setSomething();
    return $this->something;
  }

  private function setSomething() {
    $this->something = self::something;
  }
}

class bar extends foo {

  public function xxx() {
    $this->setSomething();
    $this->something++;
    return $this->something;
  }

}
?>

However when I run the script I get the following error:

Fatal error: Call to private method foo::setSomething() from context 'bar' in test.php on line 23

It would seem that bar is not inheriting the private function setSomething(). How would I fix this without modifying the foo class?

As I stated above, the foo class is not to be modified. How else can I do this? — Kenneth Vogt, Apr 09 '12 at 06:53
You use the right tool for the job, that is, make it `protected`. — alex, Apr 09 '12 at 06:54
I understand your point however I do not have acces to change the original class. Perhaps I oversimplified the example. The original class is from another file that is merely included with require(). — Kenneth Vogt, Apr 09 '12 at 06:57
In that case the author don't want it to be available in subclass. Or didnt think about in design phase. So this is a by design rule of that parent class. — Shiplu Mokaddim, Apr 09 '12 at 07:00
Then contact the original author and make clear that you need to extend the class. — deceze, Apr 09 '12 at 07:01
Oh well, I was trying to do something that is clearly beyond the original design scope. I would hate to say they didn't think about it, I don't think they could have anticipated what I have in mind. — Kenneth Vogt, Apr 09 '12 at 07:06
Just write your own method, if you can't set the original class's method to `protected`. — s3c, Apr 16 '22 at 09:22

Shiplu Mokaddim · Answer 1 · 2012-04-09T07:12:35.767

15

No, you can not fix this without modifying the foo class. Because an inherited class can not access parent class's private members. It's a very basic oop rule.

Declare setSomething() as protected. It'll be solved.

See manual

edited Apr 09 '12 at 07:12

answered Apr 09 '12 at 06:52

Shiplu Mokaddim

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As I stated above, the foo class is not to be modified. How else can I do this? – Kenneth Vogt Apr 09 '12 at 06:53
You can not do it as long as maintain oop. – Shiplu Mokaddim Apr 09 '12 at 06:59
1

So private inheritance in C++ is not real OOP? I do not agree. – jlh Jul 05 '19 at 11:32

score 8 · Answer 2 · answered Apr 09 '12 at 06:51

8

Private members are not inheritable, you can not use them in sub class. They are not accessible outside the class.

You must need to make that function as protected or public. Protected members are accessible to that class and for the inherited class. So, your best bet is to make that function Protected.

answered Apr 09 '12 at 06:51

Shakti Singh

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As I stated above, the foo class is not to be modified. How else can I do this? – Kenneth Vogt Apr 09 '12 at 06:54
1

@KennethVogt: You don't have choices here. – Shakti Singh Apr 09 '12 at 06:55

score 7 · Accepted Answer · answered Apr 09 '12 at 06:54

7

bar is inheriting the function alright, but it can't call it. That's the whole point of private methods, only the declaring class can call them.

answered Apr 09 '12 at 06:54

deceze

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So I would have to explicitly redefine setSomething() in my bar class? – Kenneth Vogt Apr 09 '12 at 06:55
1

Yes, that's the *sane* method to do this. – deceze Apr 09 '12 at 06:58
7

Better method is to use protected in the parent class ;) that way it stays private from outside, but "child" class can access it. – jave.web May 29 '15 at 10:05

score 4 · Answer 4 · edited May 23 '17 at 11:54

4

Try reflection

http://php.net/manual/en/class.reflectionclass.php

Also:

Call private methods and private properties from outside a class in PHP

edited May 23 '17 at 11:54

Community

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answered Apr 09 '12 at 06:57

zad

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Wow, that scared me into not getting too fancy. Nice info though. – Kenneth Vogt Apr 09 '12 at 07:01

score 1 · Answer 5 · answered Oct 16 '15 at 21:12

Did you try this?

class bar extends foo {

    public function xxx() {
      $this->something = parent::xxx();
      $this->something++;
      return $this->something;
    }
}

Note the parent::xxx(); is public, so it should work... even though it looks like a static call.

score 0 · Answer 6 · answered Apr 09 '12 at 06:55

0

Without modifying the original class, there is no way for the inherited class to directly call private methods of the parent class.

answered Apr 09 '12 at 06:55

Christian Mann

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How can a PHP class that extends another inherit a private function?

6 Answers6