Why Readonly classes in PHP? - Purpose & Use Cases

The Big Idea

What if your data could protect itself from accidental changes without extra code?

The Scenario

Imagine you have a class representing a user profile, and you want to make sure once the profile is created, its data never changes accidentally throughout your program.

The Problem

Manually checking and preventing changes to each property everywhere in your code is slow and error-prone. You might forget to add checks, leading to bugs that are hard to find.

The Solution

Readonly classes let you declare that all properties cannot be changed after creation, so PHP enforces this automatically, saving you from writing extra code and preventing accidental changes.

Before vs After

✗ Before

$user->name = 'Alice';
// Later in code
$user->name = 'Bob'; // Oops, changed by mistake!

✓ After

readonly class User {
  public string $name;
  public function __construct(string $name) {
    $this->name = $name;
  }
}
// Now, trying to change $user->name will cause an error

What It Enables

You can trust your objects to stay consistent and unchanged, making your code safer and easier to understand.

Real Life Example

In a banking app, account details like account number or creation date should never change after creation. Readonly classes ensure this data stays fixed.

Key Takeaways

Readonly classes prevent accidental changes to object properties.

They reduce bugs by enforcing immutability automatically.

They make your code safer and easier to maintain.