How to Update to PHP 7.4 Typed Property Without BC Break with Rector

Typed Property is one of the PHP 7.4 feature that allow to write that previously like this:

namespace Lib;

class SomeClass
{
    /** @var int */
    public $a;

    /** @var string */
    protected $b;

    /** @var bool */
    private $c;
}

to this:

namespace Lib;

class SomeClass
{
    public int $a;

    protected string $b;

    private bool $c;
}

If you follow Semver for versioning, and you don’t want to update to major change, eg: version 1 to version 2, changing this will make Break Backward Compatibility, for example:

namespace Lib;

class SomeClass
{
    protected string $b;
}

has child in application consumer:

namespace App;

use Lib\SomeClass;

class AChild extends SomeClass
{
    protected $b;
}

will result a fatal error:

Fatal error: Type of AChild::$b must be string (as in class SomeClass)

see https://3v4l.org/X9Yvd . To avoid that, you should only change to private modifier only, so, the change will only to private property:

namespace Lib;

class SomeClass
{
    /** @var int */
    public $a;

    /** @var string */
    protected $b;

-    /** @var bool */
-    private $c;
+    private bool $c;
}

Want to automate that? You can use Rector for it. First, let say, we have a re-usable package that can be consumed in our applications, with the following package structure:

lib
├── composer.json
├── composer.lock
├── src
│   └── SomeClass.php

with composer.json config like this:

{
    "require": {
        "php": "^7.4"
    },
    "autoload": {
        "psr-4": {
            "Lib\\": "src/"
        }
    }
}

Your package will be hosted in packagist or your own server.

Now, what you need is require the rector as dev dependency by go to lib directory:

cd lib/
composer require --dev rector/rector

Rector has rule named TypedPropertyRector, that part of SetList::PHP_74 constant.

It default will update all modifiers:

• public
• protected
• private

If you are using on projects that not re-usable project, you can just use SetList::PHP_74 constant as is.

For our use case, you can override it by configure it to only apply to private property only.

You can create a rector.php configuration inside the root of lib directory as follow:

<?php

declare(strict_types=1);

use Rector\Core\Configuration\Option;
use Rector\Core\ValueObject\PhpVersion;
use Rector\Php74\Rector\Property\TypedPropertyRector;
use Rector\Set\ValueObject\SetList;
use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;

return static function (ContainerConfigurator $containerConfigurator): void {
    $parameters = $containerConfigurator->parameters();
    $parameters->set(Option::PATHS, [
        __DIR__ . '/src'
    ]);
    $parameters->set(Option::PHP_VERSION_FEATURES, PhpVersion::PHP_74);

    // import php 7.4 set list for php 7.4 features
    $containerConfigurator->import(SetList::PHP_74);

    // set Typed Property only for private property
    $services = $containerConfigurator->services();
    $services->set(TypedPropertyRector::class)
        ->call('configure', [[
            TypedPropertyRector::PRIVATE_PROPERTY_ONLY => true,
        ]]);
};

Above, we import php 7.4 set list, with configured TypedPropertyRector for update to typed property to only change private property only.

Now, let’s run rector to see the diff and verify:

cd lib
vendor/bin/rector --dry-run

Everything seems correct! Let’s apply the change:

cd lib
vendor/bin/rector

Now, you have typed property in your code!

That’s it!