pipe.byRef

Code example

<?php declare(strict_types = 1);

function modify(string &$s): void
{
	$s = strtoupper($s);
}

$result = 'hello' |> modify(...);

Why is it reported?

The pipe operator |> passes the left-hand side as the first argument to the callable on the right. This value is passed by value, not by reference. When the callable declares its first parameter as pass-by-reference (&), the pipe operator cannot fulfil that contract, so PHPStan reports an error.

How to fix it

Change the callable to accept its first parameter by value instead of by reference, and return the result:

 <?php declare(strict_types = 1);

-function modify(string &$s): void
+function modify(string $s): string
 {
-	$s = strtoupper($s);
+	return strtoupper($s);
 }

 $result = 'hello' |> modify(...);