Method Chaining and Class Inheritance

Question

I think I have more or less managed to get a grasp on OOP/Inheritance, and the basics of method chaining I think I understood as well. However I am still confused about how to actually use some of it.

I wanted to do something that I've seen when working with Magento before: In Magento, I've seen some sort of "selector-function" used in method chaining. It's a little hard to put into words, but it was something along the lines of:

$categoryName = Mage::getModel('catalog/category')->load($categoryId)->getName();

It's the load($categoryId) part that interests me, as in, a function that selects some instance of something and allows me to run a function on that specific instance.

Now, I am writing a module that allows me to configure certain promotions on our website. Seeing as we'll have many different promotions and I want them to be easily configurable and modifiable, I wanted to do something similar.

So, if I wanted to be able to do something like this:

$prm = new Promotion();

$prm->addPromo('xmasPromo');
$prm->addPromo('nyPromo');

$prm->getPromo('xmasPromo')->setName('Promotion for Xmas!');
$prm->getPromo('nyPromo')->setName('Promotion for New Years!');

echo $prm->getPromo('xmasPromo')->getName(); // returns: Promotion for Xmas!
echo $prm->getPromo('nyPromo')->getName(); // returns: Promotion for New Years!

How would the class definition for that have to look like?

This may be much more simple or much more complicated than I anticipate. In either case, thanks a lot!

---

Edit: So I did some testing around with the info deceze gave me, but I'm still confused. Bad naming and putting 2 classes in 1 file aside, here's what I did:

class file:

class Promotion {
    private $__arr = array();
    public function addPromo($name) {
        $this->__arr[$name] = new Promo();
    }
    public function getPromo($name) {
        $this->__arr[$name];
    }
}

class Promo {
    private $name;
    public function setName($name) {
        $this->name = $name;
    }
    public function getName() {
        return $name;
    }
}

and the run file:

require_once 'class.php';
error_reporting(E_ALL);

$prm = new Promotion();

$prm->addPromo('xmasPromo');
$prm->addPromo('nyPromo');

$prm->getPromo('xmasPromo')->setName('Promotion for Xmas!');
$prm->getPromo('nyPromo')->setName('Promotion for New Years!');

echo 'X: '.$prm->getPromo('xmasPromo')->getName(); // returns: Promotion for Xmas!
echo "\n";
echo 'N: '.$prm->getPromo('nyPromo')->getName(); // returns: Promotion for New Years!

This gives me Fatal error: Call to a member function setName() on a non-object in /var/www/test/index.php on line 11. But why? Shouldn't getPromo() give me back the object? Thanks again..

---

Thanks to the great guys here, it works now. In case anyone were to pass by here with the same or a similar question, here's the final, working code:

Classes:

class Promotion {
    private $__arr = array();
    public function addPromo($name) {
        $this->__arr[$name] = new Promo();
    }
    public function getPromo($name) {
        return $this->__arr[$name];
    }
}

class Promo {
    private $name;
    public function setName($name) {
        $this->name = $name;
    }
    public function getName() {
        return $this->name;
    }
}

Test file:

require_once 'class.php';
error_reporting(E_ALL);

$prm = new Promotion();

$prm->addPromo('xmasPromo');
$prm->addPromo('nyPromo');

$prm->getPromo('xmasPromo')->setName('Promotion for Xmas!');
$prm->getPromo('nyPromo')->setName('Promotion for New Years!');

echo 'X: '.$prm->getPromo('xmasPromo')->getName(); // returns: Promotion for Xmas!
echo "\n";
echo 'N: '.$prm->getPromo('nyPromo')->getName(); // returns: Promotion for New Years!

Answer 1

Method chaining is really simple, all it does is use one particular element of PHP's syntax:

When a function returns an object, you can directly continue with -> after that function.

The longhand version can be:

$bar = $foo->bar();
$baz = $bar->baz();
echo $baz;

$foo->bar() returns an object ($bar) which has a method baz(), and that method returns some value ($baz). This can be written in shorthand like so:

echo $foo->bar()->baz();

$foo->bar() still returns an object which has a method baz(), so you can directly call it without assigning it to an intermediate variable. Maybe this makes it more obvious:

echo ( $foo->bar() )->baz();

You're calling the baz() method on whatever $foo->bar() returns.

$prm->getPromo('xmasPromo')->setName('Promotion for Xmas!');

As such, in your above case, all you need to do is to return an object which has the method setName from getPromo. I would assume getPromo is supposed to return some object of, say, the Promo class. If the Promo class has a method setName, you're all set.