[SOLVED] How to tell psalm to save getter state if property wasn't modified before the further checks?

How to tell psalm to save getter state if property wasn't modified before the further checks?

class A
{
    private ?string $x = null;

    public function getX(): ?null
    {
        return $this->x;
    }
}

class B
{
    public function __construct(string $y)
    {
        // Property initialization...
    }
}

$a = new A();
if ($a->getX() !== null) {
    $b = new B($a->getX());
}

For this code snippet psalm will return an error like PossiblyNullOperand or similar. I know that this is kind of an expected behavior, and can be fixed like this:

$a = new A();
if (($x = $a->getX()) !== null) {
    $b = new B($x);
}

But is there a configuration parameter in psalm, which will ignore these errors for methods like getters which always return the same result?

Psalm version: 4.18.x

Solution

Psalm need to know that the function has a consistent return value.

This is something you can describe with @psalm-mutation-free: https://psalm.dev/r/e3906e5985