Factory Method

factory-method.md

Taking our hiring manager example above. First of all we have an interviewer interface and some implementations for it

interface Interviewer {
    public function askQuestions();
}

class Developer implements Interviewer {
    public function askQuestions() {
        echo 'Asking about design patterns!';
    }
}

class CommunityExecutive implements Interviewer {
    public function askQuestions() {
        echo 'Asking about community building';
    }
}

Now let us create our HiringManager

abstract class HiringManager {
    
    // Factory method
    abstract public function makeInterviewer() : Interviewer;
    
    public function takeInterview() {
        $interviewer = $this->makeInterviewer();
        $interviewer->askQuestions();
    }
}

Now any child can extend it and provide the required interviewer

class DevelopmentManager extends HiringManager {
    public function makeInterviewer() : Interviewer {
        return new Developer();
    }
}

class MarketingManager extends HiringManager {
    public function makeInterviewer() : Interviewer {
        return new CommunityExecutive();
    }
}

and then it can be used as

$devManager = new DevelopmentManager();
$devManager->takeInterview(); // Output: Asking about design patterns

$marketingManager = new MarketingManager();
$marketingManager->takeInterview(); // Output: Asking about community building.

When to use?

Useful when there is some generic processing in a class but the required sub-class is dynamically decided at runtime. Or putting it in other words, when the client doesn't know what exact sub-class it might need.