Automate PHP Readonly Class Refactoring with Rector

Use Rector rules to automatically convert immutable DTOs and value objects into native PHP 8.2 readonly classes.

Manually adding readonly keywords across dozens of data transfer objects (DTOs) and value objects is repetitive.

Rector automates upgrading class declarations across your codebase using AST refactoring.

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Configuration

Register ReadOnlyClassRector in rector.php:

// rector.php
use Rector\Config\RectorConfig;
use Rector\Php82\Rector\Class_\ReadOnlyClassRector;

return RectorConfig::configure()
    ->withRules([
        ReadOnlyClassRector::class,
    ]);

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What It Refactors

// Before Rector (individual readonly properties):
class UserData
{
    public function __construct(
        public readonly string $name,
        public readonly string $email,
    ) {}
}

// After Rector (PHP 8.2+ native readonly class):
readonly class UserData
{
    public function __construct(
        public string $name,
        public string $email,
    ) {}
}

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Key Benefits

• Compiler-Level Immutability: Enforces that all properties cannot be modified after instantiation.
• Cleaner Constructors: Removes repetitive readonly property declarations in favor of a single class-level keyword.
• Safe Automation: Rector verifies property usage before promoting classes, ensuring mutable entities are not broken.