make assigning property via reference impure

[schlndh]

Fixes https://phpstan.org/r/cbe5c7f9-f5bd-4101-8cf6-37b7732946d4

I set certain = false, because theoretically the referenced variable may already be set, and the reference may never be written. In which case it would be pure. But I can't imagine why the reference would be used in such a way in the first place.

[ondrejmirtes]

Should be true, right? There isn't a case where this might still be pure.

[schlndh]

It could be pure:

I set certain = false, because theoretically the referenced variable may already be set, and the reference may never be written. In which case it would be pure. But I can't imagine why the reference would be used in such a way in the first place.

<?php

class Foo
{
    public ?int $foo;
    
    public function bar(): void
    {
        $x = &$this->foo;
    }
}

$foo = new Foo;
$foo->foo = 5;
$foo->bar();
var_dump($foo->foo);

[ondrejmirtes]

Alright, cool :)

[ondrejmirtes]

Thank you!