decorator.md

Decorator Design Pattern

The Decorator Pattern allows to attach new behavior by placing them inside a wrapper object that contains the behavior.

How to apply

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

class TextBook implements Book
{
    public function __construct(private string $title,) {}

    public function describe(): string
    {
        return $this->title;
    }
}

class CollectorEditionDecorator implements Book
{
    public function __construct(private Book $book) {}

    public function describe(): string
    {
        return $this->book->describe() . ", Collector edition";
    }
}

Usage:

$book = new TextBook("The Lord of the Rings");
echo $book->describe();

$edition = new CollectorEditionDecorator($book);
echo $edition->describe();

Output:

The Lord of the Rings
The Lord of the Rings, Collector edition