Question

I’m still a novice when it comes to polymorphism so I hope I can phrase my question correctly.

Let’s say I have tables in my Database – Dog, Cat and Mouse. I want to be able to call something like:

$animal = new Animal("dog", 12);

with the animal class being something like:

class Animal {
  protected $id;
  protected $legs;
  protected $height;
  function __construct($type, $id) {
    if ($type == "dog") {
      return new Dog($id);
    }
  }
}

class Dog extends Animal {
  function __construct($id) {
    $this->id = $id;
    $this->legs = 4;
    $this->height = 1;
  }
}

This doesn’t work but I want to be able to call a new Animal and pass in the specific animal and have it be returned. How can I design this? (I’m using PHP).

Answer 1

What you’re looking for is actually a design pattern called the Factory Pattern. You can read up on it here:

Factory Pattern

And some longer articles for PHP:

Design Patterns in PHP
The Basics of Using Factory Pattern in PHP