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

Posted in php, Rector, Teknologi by samsonasik on September 29, 2021

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:

├── 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:



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

    // set Typed Property only for private property
    $services = $containerConfigurator->services();
        ->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

Now, you have typed property in your code!

That’s it!

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