Decorator Pattern

The Decorator Pattern is a structural design pattern that allows you to dynamically add new behavior to an object without modifying its original class.

It follows the principle:

“Composition over inheritance”

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Real Life Example

Think about a Coffee Shop ☕

You start with:

• Basic Coffee

Then you can add:

• Milk

• Sugar

• Chocolate

Instead of creating many subclasses like:

MilkCoffee
SugarCoffee
MilkSugarCoffee
ChocolateMilkCoffee

Decorator Pattern adds features dynamically.

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Structure

Component
 ├── Concrete Component
 └── Decorator
       └── Concrete Decorators

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Laravel / PHP Example

Scenario

We are building a notification system.

Base notification:

• Simple message

Extra features:

• Email logging

• SMS logging

• Database logging

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Step 1: Component Interface

interface Notification
{
    public function send(): string;
}

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Step 2: Concrete Component

Basic notification.

class BasicNotification implements Notification
{
    public function send(): string
    {
        return "Sending notification";
    }
}

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Step 3: Base Decorator

abstract class NotificationDecorator implements Notification
{
    protected Notification $notification;

    public function __construct(Notification $notification)
    {
        $this->notification = $notification;
    }

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

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Step 4: Concrete Decorators

Email Decorator

class EmailDecorator extends NotificationDecorator
{
    public function send(): string
    {
        return $this->notification->send() . " + Email Sent";
    }
}

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SMS Decorator

class SmsDecorator extends NotificationDecorator
{
    public function send(): string
    {
        return $this->notification->send() . " + SMS Sent";
    }
}

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Database Log Decorator

class DatabaseLoggerDecorator extends NotificationDecorator
{
    public function send(): string
    {
        return $this->notification->send() . " + Logged to Database";
    }
}

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Step 5: Usage

Basic Notification

$notification = new BasicNotification();

echo $notification->send();

Output

Sending notification

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Add Email Feature

$notification = new EmailDecorator(
    new BasicNotification()
);

echo $notification->send();

Output

Sending notification + Email Sent

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Add Multiple Features

$notification = new SmsDecorator(
    new EmailDecorator(
        new DatabaseLoggerDecorator(
            new BasicNotification()
        )
    )
);

echo $notification->send();

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Output

Sending notification + Logged to Database + Email Sent + SMS Sent

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How Decorator Works

Each decorator wraps another object.

BasicNotification
    ↓
DatabaseDecorator
    ↓
EmailDecorator
    ↓
SmsDecorator

Each layer adds new behavior.

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Advantages

1. Dynamic Behavior Addition

Add features at runtime.

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2. Avoids Massive Inheritance

Without decorator:

EmailSmsNotification
EmailDatabaseNotification
SmsDatabaseNotification

Too many classes.

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3. Follows Open/Closed Principle

Open for extension, closed for modification.

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Real Laravel Use Cases

Use Case	Example
Middleware	Request decoration
Logging	Add logging dynamically
Cache	Cache wrapper
Notifications	Multi-channel notifications
API Response	Response formatting

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Decorator vs Composite

Decorator	Composite
Adds behavior	Builds tree structure
Wraps single object	Manages child objects
Focus on enhancement	Focus on hierarchy

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Decorator vs Inheritance

Decorator	Inheritance
Runtime flexibility	Compile-time structure
Composition based	Class hierarchy
More scalable	Can create class explosion

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When to Use Decorator Pattern

Use Decorator Pattern when:

✅ You want to add features dynamically ✅ You want flexible object enhancement ✅ You want to avoid subclass explosion ✅ Features can be combined independently

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Short Interview Definition

The Decorator Pattern dynamically adds new behavior to objects by wrapping them inside decorator classes without modifying the original object.