Question

I’m stuck with a behaviour of PHP which I can’t seem to understand.

class A {
    private $v;
    public function __construct(&$v)
    {
        $this->v = &$v;
    }

    public function setV($v) {
        $this->v = $v;
    }

    public function getV() {
        return $this->v;
    }
}

class B extends A {
    public function setV($v) {
        $this->v = $v;
    }
}

$v = '1';
$c = new A($v); // <= this will be replaced

echo $c->getV() . "\n";
$v = '2';
echo $c->getV() . "\n";
$c->setV('3');
echo $c->getV() . "\n";
echo $v . "\n";

Outputs

1
2
3
3

But when I replace the object creation with $c = new B($v); it outputs

1
2
2
2

I would expect the same output as before. Why is this? I use PHP 5.3 but probably update to try to fix this.

Answer 1

When a class extends another parent class it can only use public and protected variables and functions from the parent class..
So this will print the same result ;

<?php

class A {
 private $v;
  public function __construct(&$v)
  {
    $this->v = &$v;
  }

  public function setV($v) {
    $this->v = $v;
  }

 public function getV() {
    return $this->v;
  }
}

class B extends A {
    public function setV($v) {
        parent::setV($v);
    }
}

$v = '1';
$c = new B($v); // <= this will be replaced

echo $c->getV() . "\n";
$v = '2';
echo $c->getV() . "\n";
$c->setV('3');
echo $c->getV() . "\n";
echo $v . "\n";

?>