PHP Decorator Pattern

A short screencast: the Decorator pattern in PHP — wrap an object and add behavior on the fly. A notification chain: email → sms → slack.

Decorator Pattern — open the lesson page

Overview

The Decorator lets you dynamically add responsibilities to an object without modifying its class. We define a common NotifierInterface, a base EmailNotifier, and an abstract NotifierDecorator that holds the wrapped object. Concrete decorators SmsDecorator and SlackDecorator extend the behavior by wrapping each other — forming a call chain.

UML diagram

classDiagram class NotifierInterface { <<interface>> +send(message: string): string } class EmailNotifier { +send(message: string): string } class NotifierDecorator { #wrapped: NotifierInterface +__construct(wrapped: NotifierInterface) +send(message: string): string } class SmsDecorator { +send(message: string): string } class SlackDecorator { +send(message: string): string } NotifierInterface <|-- EmailNotifier : implements NotifierInterface <|-- NotifierDecorator : implements NotifierDecorator <|-- SmsDecorator : extends NotifierDecorator <|-- SlackDecorator : extends NotifierDecorator o-- NotifierInterface : wrapped

Code

NotifierInterface.php

interface NotifierInterface
{
    public function send(string $message): string;
}

EmailNotifier.php

class EmailNotifier implements NotifierInterface
{
    public function send(string $message): string
    {
        return "email: $message";
    }
}

NotifierDecorator.php

class NotifierDecorator implements NotifierInterface
{
    protected NotifierInterface $wrapped;

    public function __construct(NotifierInterface $wrapped)
    {
        $this->wrapped = $wrapped;
    }

    public function send(string $message): string
    {
        return $this->wrapped->send($message);
    }
}

SmsDecorator.php

class SmsDecorator extends NotifierDecorator
{
    public function send(string $message): string
    {
        return $this->wrapped->send($message).' | sms: '.$message;
    }
}

SlackDecorator.php

class SlackDecorator extends NotifierDecorator
{
    public function send(string $message): string
    {
        return $this->wrapped->send($message).' | slack: '.$message;
    }
}

demo.php

require_once 'NotifierInterface.php';
require_once 'EmailNotifier.php';
require_once 'NotifierDecorator.php';
require_once 'SmsDecorator.php';
require_once 'SlackDecorator.php';

$notifier = new SlackDecorator(
    new SmsDecorator(
        new EmailNotifier()
    )
);

echo $notifier->send('order ready').PHP_EOL;

Example output

Running php demo.php in the terminal prints the notification chain:

email: order ready | sms: order ready | slack: order ready

Advantages

Adds behaviour without subclassing or editing the original class.
Decorators combine freely and stack in any order.
Behaviour can be turned on and off at runtime.
Each decorator is responsible for a single concern.

When to use

When responsibilities must be added to an object dynamically.
When inheritance would lead to an explosion of subclasses.
When the behaviours are independent and combine.
When the original class cannot be changed (third-party or final).

Usage in Laravel

In Laravel the decorator is the cache repository: Illuminate\Cache\Repository wraps a store (Illuminate\Contracts\Cache\Store) and adds remember(), tags and events on top without touching the driver. Log channels in Illuminate\Log\LogManager and the wrappers around the HTTP client are built the same way: behaviour is layered on.