Calling constructors thru several levels of inherited classes

bunner_bob

I have a class which extends another class which extends yet another class. I'm wondering what the best way would be to call constructors in each of those classes - using parent::parentconstructor(), or some other method?

e.g.

class One {
    function One () {
        // set some properties
    }
}

Class Two extends One {
    function Two() {
        parent::One();
        // additional properties, perhaps some methods
    }
}

Class Three extends Two {
    function Three() {
        parent::Two();
        // more properties & methods
    }
}

Or are there other ways to go about this, or any caveats for this way of doing things?

Thanks,
Bob

eoghain

If you aren't using PHP 5 then this is the way you have to do it.

dalecosp

I don't think there is any other way in v5 either; AAMOF, I thought PHP was "single inheritance"* ... this is a "level inheritance" model. I assume, though, that "level inheritance" is possible if Bob's code is working.... <?>

😕

*and I have it on fairly good authority...

eoghain

Single inheritance doesn't mean something can only be inherited once. I have the same structure that bob has for some of my code, object inherited from object inherited from object, single inheritance means you can't have an object inherit from more than 1 object. Languages like Java and c# get around this with the concept of interfaces where you can inherit multiple interfaces because interfaces don't have any implementation.

bubblenut

In PHP5 you can use the parent::__construct() syntax. The only way of emulating this in PHP4 is a little more cumbersome.

class ClassTwo extends ClassOne {
  function ClassTwo() {
    $parent = get_parent_class($this);
    parent::$parent();
  }
}

This means that get_parent_class() is called on every instantiation of the class.

Spot the guy who just got his copy of Upgrading to PHP5 through the post :p

eoghain

Nice, maybe some day my company will allow me to upgrade to PHP 5. Unfortunatly I don't think it's going to be very soon.

dalecosp

Originally posted by eoghain
Single inheritance doesn't mean something can only be inherited once. I have the same structure that bob has for some of my code, object inherited from object inherited from object, single inheritance means you can't have an object inherit from more than 1 object. Languages like Java and c# get around this with the concept of interfaces where you can inherit multiple interfaces because interfaces don't have any implementation.

Thanks for that. I guess my definition is either too strict, or just plain wrong. IIRC, you can "multiply inherit" in C++. My Java skills are weak, and C# virtually null (pun intended), although I was somewhat aware of the "workaround" concept ... either way, I appreciate the info. The "grandparent-parent-child" relationship is what I call/learned as "level inheritance". If PHP can do that, so much the better. 🆒

/me is another guy just learning v5... and trying to get my tired brain wrapped around OOP... :queasy:

bunner_bob

Thanks bubblenut, everyone - I'll mark this resolved, though I haven't tried it yet.

I'm doing a major reconfig of a site that I built knowing less than I do now, and running constructors on my chain of inherited classes is part of making it work. I've been working from a separate file of site-specific variables and more generic classes (with the idea of making them more portable) but I've ended up with a million calls to "$GLOBALS['this']" and "$GLOBALS['that']", which feels clumsy. This will allow me to move variables into each class and set them via constructor in each class - a more logical arrangement.

Won't be quite as easy to repurpose, as I'll have to go through each class and make changes, but I can still organize all my variables at the top to make them easy to find.

Bob
(always slightly less dumb than the day before...)