Why does PHP not automatically call parent constructors?

Question

Fairly straightforward question. In C++ the parent constructor will be implicitly called before the child constructor, so what logic is there for PHP not to do things this way?

EDIT: I've got a good answer from Lukman, but I was hoping for more of a reason why there is a difference. Maybe the question should be why does C++ not allow custom calling of parent constructors? I guess that's another question though.

Answer 1

I think it's a good thing that PHP makes you call parent's constructor manually, because it allows child's constructor such as following:

public function __construct() {    // set up variables that parent::__construct() requires    $var1 = get_stuff_from_db();    $var2 = get_stuff_from_webservice();     parent::__construct($var1, $var2);     // continue setting up $this var    $this->default = 'Default';    $this->do_some_secret_stuff(); } 

Or even:

public function __construct($param) {    // call differently based on condition    if (is_array($param))       $param['id'] = 0;       parent::__construct($param);    }    else {       parent::__construct($param, 0, TRUE);    }     // continue setting up $this var    $this->default = 'Default';    $this->do_some_secret_stuff(); } 

Meaning, you are free to call the parent constructor anywhere within the child's and you are free to do stuff before and after the call. Ain't that a feature indeed?

Answer 2

When you don't have a constructor in the child class, then the parent one is automatically called.

If you decided to add a constructor to the child class, then of course you need to explicitly call the parent constructor. If you are already taking the time to add a constructor to your child class, then adding one more line of code parent::__construct(); doesn't seem to be a big deal. But the overriding is actually a convenient flexibility.