builder.md

Builder Design Pattern

The Builder design pattern is used to construct complex objects step by step. It allows you to create different representations of the same object using the same construction process.

# How to apply

class Book
{
    public function __construct(
        public string $title,
        public string $author,
        public ?string $genre = null,
        public ?float $price = null,
    ) {}

    public function getDescription(): string
    {
        return sprintf(
            "Title: %s, Author: %s, Genre: %s, Price: %s",
            $this->title,
            $this->author,
            $this->genre ?? 'N/A',
            $this->price ?? 'N/A'
        );
    }
}

class BookBuilder
{
    private ?string $title = null;
    private ?string $author = null;
    private ?string $genre = null;
    private ?float $price = null;

    public function setTitle(string $title): self
    {
        $this->title = $title;
        return $this;
    }

    public function setAuthor(string $author): self
    {
        $this->author = $author;
        return $this;
    }

    public function setGenre(string $genre): self
    {
        $this->genre = $genre;
        return $this;
    }

    public function setPrice(float $price): self
    {
        $this->price = $price;
        return $this;
    }

    public function build(): Book
    {
        return new Book(
            $this->title,
            $this->author,
            $this->genre,
            $this->price
        );
    }
}

Usage:

$builder = new BookBuilder();
$book = $builder
    ->setTitle("The Martian")
    ->setAuthor("Andy Weir")
    ->setGenre("Science Fiction")
    ->setPrice(14.99)
    ->build();

echo $book->getDescription();

Output:

Title: The Martian, Author: Andy Weir, Genre: Science Fiction, Price: 14.99

Improvement:

BookDirector builds different books from the same BookBuilder class. That helps to hide complex building process and reduce repetitive works.

class BookDirector {
    public function buildFantasyBook(BookBuilder $builder): Book
    {
        return $builder
            ->setTitle("The Hobbit")
            ->setAuthor("J.R.R. Tolkien")
            ->setGenre("Fantasy")
            ->setPrice(19.99)
            ->build();
    }

    public function buildSciFiBook(BookBuilder $builder): Book
    {
        return $builder
            ->setTitle("The Martian")
            ->setAuthor("Andy Weir")
            ->setGenre("Science Fiction")
            ->setPrice(14.99)
            ->build();
    }
}

Usage:

$builder = new BookBuilder();
$director = new BookDirector();

$fantasyBook = $director->buildFantasyBook($builder);
echo $fantasyBook->getDescription();

$sciFiBook = $director->buildSciFiBook($builder);
echo $sciFiBook->getDescription();

Output:

Title: The Hobbit, Author: J.R.R. Tolkien, Genre: Fantasy, Price: 19.99
Title: The Martian, Author: Andy Weir, Genre: Science Fiction, Price: 14.99