PHP object inheritance : how to access parent attributes?

Question

I wrote this little test script for PHP object inheritance :

<?php

class A {
    protected $attr;

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

    public function getAttr() {
        return $this->attr;
    }
}

class B extends A {

}

$b = new B(5);
echo $b->getAttr();

This displays nothing! Why doesn't it display 5? Isn't class B supposed to be like class A?

bwoebi · Accepted Answer · 2013-06-16 13:50:18Z

4

The error is here:

$this->$attr = $attr;

you assign here to $this->{5} (the value of $attr).

Write, to address the property:

$this->attr = $attr;
//     ^------ please note the removed `$` sign

To notice what is going on in such cases, try to dump your object: var_dump($b);

answered Jun 16, 2013 at 13:50

bwoebi

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2 Comments

mimipc Over a year ago

Thanks for your answer. I'm very well aware about that, but sometimes you just fail to see a typo, even after checking 10 times...

mimipc Over a year ago

Just because sleep doesn't... ^^

Baba · Accepted Answer · 2013-06-16 13:49:46Z

2

You are using variable variable instead of accessing the variable directly

 $this->$attr = $attr;
        ^
        |----- Remove This

With

 $this->attr = $attr;

answered Jun 16, 2013 at 13:49

Baba

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2 Comments

mimipc Over a year ago

Wooow! I was very disapointed, but now I feel like an idiot! Thanks a lot!

Baba Over a year ago

Leave the system , Play some games GOW is nice .. Take a nap then continue programming ... This fix most similar programming errors

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