Abstract Factory

abstract-factory.md

Translating the door example above. First of all we have our Door interface and some implementation for it

interface Door {
    public function getDescription();
}

class WoodenDoor implements Door {
    public function getDescription() {
        echo 'I am a wooden door';
    }
}

class IronDoor implements Door {
    public function getDescription() {
        echo 'I am an iron door';
    }
}

Then we have some fitting experts for each door type

interface DoorFittingExpert {
    public function getDescription();
}

class Welder implements DoorFittingExpert {
    public function getDescription() {
        echo 'I can only fit iron doors';
    }
}

class Carpenter implements DoorFittingExpert {
    public function getDescription() {
        echo 'I can only fit wooden doors';
    }
}

Now we have our abstract factory that would let us make family of related objects i.e. wooden door factory would create a wooden door and wooden door fitting expert and iron door factory would create an iron door and iron door fitting expert

interface DoorFactory {
    public function makeDoor() : Door;
    public function makeFittingExpert() : DoorFittingExpert;
}

// Wooden factory to return carpenter and wooden door
class WoodenDoorFactory implements DoorFactory {
    public function makeDoor() : Door {
        return new WoodenDoor();
    }

    public function makeFittingExpert() : DoorFittingExpert{
        return new Carpenter();
    }
}

// Iron door factory to get iron door and the relevant fitting expert
class IronDoorFactory implements DoorFactory {
    public function makeDoor() : Door {
        return new IronDoor();
    }

    public function makeFittingExpert() : DoorFittingExpert{
        return new Welder();
    }
}

And then it can be used as

$woodenFactory = new WoodenDoorFactory();

$door = $woodenFactory->makeDoor();
$expert = $woodenFactory->makeFittingExpert();

$door->getDescription();  // Output: I am a wooden door
$expert->getDescription(); // Output: I can only fit wooden doors

// Same for Iron Factory
$ironFactory = new IronDoorFactory();

$door = $ironFactory->makeDoor();
$expert = $ironFactory->makeFittingExpert();

$door->getDescription();  // Output: I am an iron door
$expert->getDescription(); // Output: I can only fit iron doors

As you can see the wooden door factory has encapsulated the carpenter and the wooden door also iron door factory has encapsulated the iron door and welder. And thus it had helped us make sure that for each of the created door, we do not get a wrong fitting expert.

When to use?

When there are interrelated dependencies with not-that-simple creation logic involved