possiblyImpure.static

Code example

<?php declare(strict_types = 1);

/**
 * @phpstan-pure
 */
function getNextId(): int
{
	static $counter = 0;

	return $counter;
}

Why is it reported?

This identifier is not reported in practice because static variable usage is always considered definitely impure, not just possibly impure. PHPStan reports impure.static instead.

The function or method is marked as @phpstan-pure but uses a static variable. Static variables persist their value between function calls, which means the function relies on and can modify mutable state. Pure functions must always return the same result for the same inputs and must not depend on hidden state.

How to fix it

Replace the static variable with a parameter or a different design, or remove the @phpstan-pure annotation if the function intentionally depends on static state:

-/**
- * @phpstan-pure
- */
-function getNextId(): int
+function getNextId(int $counter): int
 {
-	static $counter = 0;
-
 	return $counter;
 }