property.readOnlyAssignByRef - Phpstan

Code example

php

<?php declare(strict_types = 1);

class Foo
{
	public function __construct(
		public readonly int $value = 42,
	) {}

	public function doFoo(): void
	{
		$ref = &$this->value;
	}
}

Why is it reported?

A readonly property cannot be assigned by reference. Creating a reference to a readonly property would allow its value to be modified through the reference variable, bypassing the readonly constraint. PHP prohibits this at the language level.

How to fix it

Copy the value instead of creating a reference:

diff-php

 <?php declare(strict_types = 1);

 class Foo
 {
 	public function __construct(
 		public readonly int $value = 42,
 	) {}

 	public function doFoo(): void
 	{
-		$ref = &$this->value;
+		$copy = $this->value;
 	}
 }