PHP Class Variable Inheritance via Class Extends

Question

I have two classes; userFunction and userDatabase:

class userDatabase {
        protected $database = 'btc.db';
        protected $short;
        protected $salt;
        function __construct(){
            $this->short = $this->salt = bin2hex(random_bytes(6));
        }
}
class userFunction extends userDatabase {
    function __construct(){
        $this->database.PHP_EOL;
        $this->short.PHP_EOL;
        $this->salt.PHP_EOL;
    }
}

$r = new userFunction;
var_dump($r);

Output is as follows:

object(userFunction)#1 (3) {
  ["database":protected]=>
  string(6) "btc.db"
  ["short":protected]=>
  NULL
  ["salt":protected]=>
  NULL
}

This isn't exactly what I was expecting. Presumably I set $this->short and $this->salt to generate a random 6 character random hex salt from binary data. I extended the userDatabase class to inherit the variables to userFunction which I expect to be able to call via $this->salt and $this->short within __construct() of userFunction. However, the variables are returned as NULL.

I've been searching for an answer to why this is, but I don't seem to be able to formulate the query correctly as I'm honestly not sure what's happening here. This seems to be a related issue, but I'm not entirely sure. Specifically, is it even possible to accomplish what I'm trying to do this particular way? Is each instance of $this->salt and $this->short the same in each class, or are they both different? How would I fix my NULL problem, here?

I appreciate the assistance.

What is $this->database.PHP_EOL supposed to be doing? It's not setting any value, it's not displaying anything — Mark Baker
– Mark Baker, Commented Jan 24, 2016 at 12:51
$this->database is actually: protected $database = 'myDatabase.db';. So it's part of my test to ensure that I can access the variables as intended cross class, which seems to be working with this particular instance, just not with $this->short or $this->salt. — zQueal
– zQueal, Commented Jan 24, 2016 at 12:53
"I have two functions..." - no, you have two classes. It may seem picky, but learning the right terms will help you find and understand help so much easier. — IMSoP
– IMSoP, Commented Jan 24, 2016 at 13:00

roippi · Accepted Answer · 2016-01-24 12:56:02Z

3

When you override __construct (or any other method) in a child, the parent's method doesn't get called - unless you explicitly do so.

class userFunction extends userDatabase {
    function __construct(){
        parent::__construct();
        $this->database.PHP_EOL;
        $this->short.PHP_EOL;
        $this->salt.PHP_EOL;
    }
}

edited Jan 24, 2016 at 12:56

answered Jan 24, 2016 at 12:54

roippi

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2 Comments

Ricardo Silva Over a year ago

yeah, I was going to say that .You have to call the parent constructor inside userFuction constructor.

zQueal Over a year ago

I feel terrible about it, but adding parent::__construct(); seems to have worked perfectly. Thanks for your time!

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