Composition over inheritance in final classes

Published on by

Composition over inheritance in final classes image

Final classes, you either love them or hate them. People have been using them more recently in their open-source packages, but what does that mean for you? How do you handle this in application code?

Developers have been discussing composition over inheritance for years, and final classes are a perfect use case. A recent example I was talking to someone about was 'moneyphp/money', which implemented final classes. Let's dive in.

Let's take the example of 'moneyphp/money' and look at how we might integrate with it. Before final classes, we would extend the Money class and use it as I need to. However, that is not possible anymore, so we want to find a way to work with it. We will create a class called MoneyImplementation which will be the class we want to use.

class MoneyImplementation
{
private Money $money;
 
public function __construct(
int|string $amount,
Currency $currency,
) {
$this->money = new Money(
amount: $amount,
currency: $currency,
);
}
}

So in the code above, we have used composition to build a class that will proxy its construction to the money class - setting a property on the class to the constructed instance. The next problem is how do we call class methods on the money class without extending the API we want to call. Without adding this, we would have to add an accessor to get the money instance from our class, and then use the accessor like the following.

$money = new MoneyImplementation(
amount: 10_000,
currency: new Currency(
code: 'USD',
),
);
 
$money->money()->getAmount();

This isn't ideal, but without any additional work, this is acceptable. But we can take it one step further using a little PHP magic. Let's add this magic method to our MoneyImplementation class.

class MoneyImplementation
{
private Money $money;
 
public function __construct(
int|string $amount,
Currency $currency,
) {
$this->money = new Money(
amount: $amount,
currency: $currency,
);
}
 
public function __call(string $name, array $arguments)
{
if (! method_exists($this->money, $name)) {
throw new RuntimeException(
message: "Method [$name] does not exist.",
);
}
 
return $this->money->{$name}(...$arguments);
}
}

We add a method __call to our class so we can proxy the call straight to the money instance we have already constructed. Before that, however, we can add a safety check to ensure the method exists. Using this, we can now simplify the API.

$money = new MoneyImplementation(
amount: 10_000,
currency: new Currency(
code: 'USD',
),
);
 
$money->getAmount();

This may not be the best example to illustrate the point as we haven't added anything to our class. However, it illustrates how we can use composition over inheritance to get around final package classes.

Have you found a workaround for this? How would you handle this scenario? Let us know on Twitter.

Steve McDougall photo

Technical writer at Laravel News, Developer Advocate at Treblle. API specialist, veteran PHP/Laravel engineer. YouTube livestreamer.

Cube

Laravel Newsletter

Join 40k+ other developers and never miss out on new tips, tutorials, and more.

image
No Compromises

Joel and Aaron, the two seasoned devs from the No Compromises podcast, are now available to hire for your Laravel project.

Visit No Compromises
Laravel Forge logo

Laravel Forge

Easily create and manage your servers and deploy your Laravel applications in seconds.

Laravel Forge
Tinkerwell logo

Tinkerwell

The must-have code runner for Laravel developers. Tinker with AI, autocompletion and instant feedback on local and production environments.

Tinkerwell
No Compromises logo

No Compromises

Joel and Aaron, the two seasoned devs from the No Compromises podcast, are now available to hire for your Laravel project. ⬧ Flat rate of $7500/mo. ⬧ No lengthy sales process. ⬧ No contracts. ⬧ 100% money back guarantee.

No Compromises
Kirschbaum logo

Kirschbaum

Providing innovation and stability to ensure your web application succeeds.

Kirschbaum
Shift logo

Shift

Running an old Laravel version? Instant, automated Laravel upgrades and code modernization to keep your applications fresh.

Shift
Bacancy logo

Bacancy

Supercharge your project with a seasoned Laravel developer with 4-6 years of experience for just $2500/month. Get 160 hours of dedicated expertise & a risk-free 15-day trial. Schedule a call now!

Bacancy
LoadForge logo

LoadForge

Easy, affordable load testing and stress tests for websites, APIs and databases.

LoadForge
Paragraph logo

Paragraph

Manage your Laravel app as if it was a CMS – edit any text on any page or in any email without touching Blade or language files.

Paragraph
Lucky Media logo

Lucky Media

Bespoke software solutions built for your business. We ♥ Laravel

Lucky Media
Lunar: Laravel E-Commerce logo

Lunar: Laravel E-Commerce

E-Commerce for Laravel. An open-source package that brings the power of modern headless e-commerce functionality to Laravel.

Lunar: Laravel E-Commerce
DocuWriter.ai logo

DocuWriter.ai

Save hours of manually writing Code Documentation, Comments & DocBlocks, Test suites and Refactoring.

DocuWriter.ai
Rector logo

Rector

Your partner for seamless Laravel upgrades, cutting costs, and accelerating innovation for successful companies

Rector

The latest

View all →
Generate Code Coverage in Laravel With PCOV image

Generate Code Coverage in Laravel With PCOV

Read article
Non-backed Enums in Database Queries and a withSchedule() bootstrap method in Laravel 11.1 image

Non-backed Enums in Database Queries and a withSchedule() bootstrap method in Laravel 11.1

Read article
Laravel Pint --bail Flag image

Laravel Pint --bail Flag

Read article
Laravel Herd for Windows is now released! image

Laravel Herd for Windows is now released!

Read article
The Laravel Worldwide Meetup is Today image

The Laravel Worldwide Meetup is Today

Read article
Cache Routes with Cloudflare in Laravel image

Cache Routes with Cloudflare in Laravel

Read article