abstract-factory.md

Abstract Factory Design Pattern

The Abstract Factory pattern lets you produce families of related or dependent objects without specifying their concrete classes.

How to apply

interface Book
{
    public function getName(): string;
}

class FantasyBook implements Book
{
    public function __construct(private string $name) {}

    public function getName(): string
    {
        return $this->name;
    }
}

class ScienceFictionBook implements Book
{
    public function __construct(private string $name) {}

    public function getName(): string
    {
        return $this->name;
    }
}

interface BookCover
{
    public function getType(): string;
}

class FantasyBookCover implements BookCover
{
    public function getType(): string
    {
        return "Fantasy book cover";
    }
}

class ScienceFictionBookCover implements BookCover
{
    public function getType(): string
    {
        return "Science fiction book cover";
    }
}

interface BookFactory
{
    public function createBook(string $name): Book;
    public function createBookCover(): BookCover;
}

class FantasyBookFactory implements BookFactory
{
    public function createBook(string $name): Book
    {
        return new FantasyBook($name);
    }

    public function createBookCover(): BookCover
    {
        return new FantasyBookCover();
    }
}

class ScienceFictionBookFactory implements BookFactory
{
    public function createBook(string $name): Book
    {
        return new ScienceFictionBook($name);
    }

    public function createBookCover(): BookCover
    {
        return new ScienceFictionBookCover();
    }
}

Usage:

$fantasyFactory = new FantasyBookFactory();
$fantasyBook = $fantasyFactory->createBook("Lord of the Rings");
$fantasyBookCover = $fantasyFactory->createBookCover();

echo $fantasyBook->getName();
echo $fantasyBookCover->getType();

$scienceFictionFactory = new ScienceFictionBookFactory();
$scienceFictionBook = $scienceFictionFactory->createBook("The Martian");
$scienceFictionBookCover = $scienceFictionFactory->createBookCover();

echo $scienceFictionBook->getName();
echo $scienceFictionBookCover->getType();

Output:

Lord of the Rings
Fantasy book cover

The Martian
Science fiction book cover

Improvement:

Here is some improvement to our code to reduce the code repeat from the previous usage section.

function createBookSet(BookFactory $factory, string $name) {
    $book = $factory->createBook($name);
    $cover = $factory->createBookCover();

    echo "{$book->getName()} with a {$cover->getType()}";
}

Usage:

$fantasyBookFactory = new FantasyBookFactory();
createBookSet($fantasyBookFactory, "Lord of the Rings");

$scienceFictionBookFactory = new ScienceFictionBookFactory();
createBookSet($scienceFictionBookFactory, "The Martian");

Output:

Lord of the Rings with a Fantasy book cover
The Martian with a Science fiction book cover