Preserving Date Integrity with Immutable Carbon

In the realm of PHP and Laravel, the nesbot/carbon package has become the go-to solution for handling date and time manipulations. With its powerful API, it provides developers with an intuitive way to work with dates. However, one crucial aspect that often goes unnoticed is the mutability of the default Carbon object. In this blog post, we will explore why adopting the CarbonImmutable object is a wise choice, especially when dealing with the Laravel framework, and how it can safeguard your application from unintended side effects.

Understanding Mutability

The default Carbon object in PHP is mutable, meaning that any changes made to a Carbon instance will directly modify the object. For instance, calling ->addDay() on a Carbon object alters its value, which might lead to undesired results if not used with caution.

The Importance of Immutability

By contrast, the CarbonImmutable object maintains data integrity by preventing changes to the original object. When you use the CarbonImmutable object, a new instance is created with the updated value, leaving the original object unchanged. Embracing immutability ensures consistency and predictability in your application's codebase, making it easier to debug and maintain.

Accidental Attribute Mutation

Consider a scenario where a DTO has a published_at property. If the default mutable Carbon is used to set the published_at property, all changes will propagate throughout the application, affecting other parts of the codebase and potentially leading to inconsistencies.

Let's dive deeper into some code examples using a Post DTO with a published_at attribute and a computed attribute is_new to illustrate the potential accidental manipulation of the published_at attribute. Assuming you have a posts table in your database with a published_at column, let's define the Post model and set up the casting for the published_at attribute:

use Carbon\Carbon;

class Post
{
    public function __construct(
        public readonly Carbon $published_at,
    ) {}

    public function is_new(): bool
    {
        return $this->published_at->addDay()->isFuture();
    }
}

The ->addDay() call manipulates the original published_at property every time you check if the post is new. This will always change the check itself - as the date moves.

Safeguarding Data Integrity

To avoid accidental attribute mutations, it is advisable to use the CarbonImmutable object when working with dates. This ensures that any modifications made to the published_at property, for instance, result in a new Carbon instance, preserving the original data.

use Carbon\CarbonImmutable;

class Post
{
    public function __construct(
        public readonly CarbonImmutable $published_at,
    ) {}

    public function is_new(): bool
    {
        return $this->published_at->addDay()->isFuture();
    }
}

This will ensure that the published_at property is really readonly and will never change it's inner value.

Preventing Accidental Database Persistence

Using the mutable Carbon object without caution could lead to inadvertent changes being persisted in the database, causing discrepancies in your data. By employing the CarbonImmutable object, you mitigate the risk of accidentally persisting unwanted changes, as the original data remains untouched.

Handling external Carbon objects

When working with external code that provides a CarbonInterface or Carbon object, ensuring immutability might seem challenging at first glance. However, achieving an immutable Carbon instance is straightforward. Simply utilize the toImmutable() method available on the Carbon instance. For instance:

use Carbon\CarbonInterface;
use Carbon\CarbonImmutable;

// Assume you receive a CarbonInterface instance from an external source
/** @var CarbonInterface $externalCarbon */
$externalCarbon = SomeExternalPackage::getCarbonInstance();

// Convert the received Carbon instance to an immutable one
$immutableCarbon = $externalCarbon->toImmutable();
// or
$immutableCarbon = CarbonImmutable::instance($externalCarbon);

By calling the toImmutable() method on a received Carbon object or using CarbonImmutable::instance(), you create a new instance that preserves the original data while ensuring immutability. This approach empowers you to maintain data integrity and avoid unintended changes throughout your application.

Conclusion

The nesbot/carbon PHP package is an invaluable tool for managing dates and times in applications. By embracing the CarbonImmutable object, you can enhance data integrity and avoid unintentional mutations, safeguarding the consistency of your application. Employing this approach throughout your codebase ensures better maintainability and reduces the likelihood of encountering data-related issues in the future. Remember, using the right practices from the outset can save hours of debugging and help create a more robust and reliable application.