property.readWrite - Phpstan

Code example

php

<?php declare(strict_types = 1);

class Base
{
	public readonly string $name;

	public function __construct(string $name)
	{
		$this->name = $name;
	}
}

class Child extends Base
{
	public string $name; // ERROR: Readwrite property Child::$name overrides readonly property Base::$name.

	public function __construct(string $name)
	{
		$this->name = $name;
	}
}

Why is it reported?

A child class declares a readwrite (non-readonly) property that overrides a readonly property from the parent class. This violates the contract established by the parent class -- the parent guarantees that the property cannot be modified after initialization, but the child removes this guarantee. This breaks the Liskov Substitution Principle because code relying on the parent type expects the property to be immutable.

How to fix it

Keep the readonly modifier on the overriding property:

diff-php

 <?php declare(strict_types = 1);

 class Child extends Base
 {
-	public string $name;
+	public readonly string $name;

 	public function __construct(string $name)
 	{
 		$this->name = $name;
 	}
 }