assign.staticPropertyProtectedSet

Code example

<?php declare(strict_types = 1);

class Foo
{
    public protected(set) static int $count = 0;
}

Foo::$count = 5;

Why is it reported?

The static property uses asymmetric visibility with protected(set), meaning it can be read publicly but can only be written to from within the declaring class or its subclasses. The code is attempting to assign a value to this property from outside the class hierarchy, which violates the write visibility restriction.

Asymmetric visibility for static properties is a PHP 8.4+ feature that allows separate read and write access levels.

How to fix it

Use a public method on the class to modify the property:

 <?php declare(strict_types = 1);

 class Foo
 {
     public protected(set) static int $count = 0;

+    public static function setCount(int $value): void
+    {
+        self::$count = $value;
+    }
 }

-Foo::$count = 5;
+Foo::setCount(5);

Or change the property's write visibility if external writes are intended:

 <?php declare(strict_types = 1);

 class Foo
 {
-    public protected(set) static int $count = 0;
+    public static int $count = 0;
 }

 Foo::$count = 5;