How do I change a readonly property using reflection in PHP 8.1?

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Is there any way, using reflection or otherwise, to change a readonly property that has already been set?

We sometimes do that in tests, and we don't want to avoid using readonly props just for testing purposes.

class Acme {
    public function __construct(
        private readonly int $changeMe,
    ) {}
}

$object= new Acme(1);
$reflectionClass = new ReflectionClass($object);
$reflectionProperty = $reflectionClass->getProperty('changeMe');
$reflectionProperty->setAccessible(true);
$reflectionProperty->setValue($object, 2);

Fatal error: Uncaught Error: Cannot modify readonly property Acme::$changeMe
php-8.1 php-8 reflection php
1 Answers

The only way I can think of to change a readonly property is to reflect the object without calling its constructor. However, not sure if it's useful in your particular case

class Acme {
    public function __construct(
        public readonly int $changeMe,
    ) {}
}

$object = new Acme(1);
$reflection = new ReflectionClass($object);
$instance = $reflection->newInstanceWithoutConstructor();
$reflectionProperty = $reflection->getProperty('changeMe');
$reflectionProperty->setValue($instance, 33);

var_dump($reflectionProperty->getValue($instance)); // 33

https://3v4l.org/mis1l#v8.1.0

Note: we are not actually "changing" the property we are just setting it for the first time since no constructor is called.

user_59993720
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