void.pure

Code example

<?php declare(strict_types = 1);

function calculate(int $a, int $b): void
{
	$result = $a + $b;
}

Why is it reported?

A function or method returns void, has no side effects, does not throw exceptions, does not modify parameters by reference, and does not have any @phpstan-assert tags. A void function without side effects is useless -- it performs computation but discards the result without affecting any observable state.

This is reported for standalone functions and private methods where PHPStan can determine that no side effects occur.

How to fix it

If the function is supposed to produce a result, return it instead of discarding it:

 <?php declare(strict_types = 1);

-function calculate(int $a, int $b): void
+function calculate(int $a, int $b): int
 {
-	$result = $a + $b;
+	return $a + $b;
 }

If the function is supposed to have side effects (e.g., writing to a file or modifying external state), add the missing side effect:

 <?php declare(strict_types = 1);

 function calculate(int $a, int $b): void
 {
 	$result = $a + $b;
+	echo $result;
 }

If the function is intentionally impure but PHPStan cannot detect the side effect, mark it explicitly:

 <?php declare(strict_types = 1);

+/** @phpstan-impure */
 function calculate(int $a, int $b): void
 {
 	$result = $a + $b;
 }