preDec.nonNumeric

Code example

<?php declare(strict_types = 1);

function doFoo(string $s): void
{
	--$s;
}

Why is it reported?

The pre-decrement operator -- is intended for numeric types. Applying it to a non-numeric value such as string, bool, null, or an object does not produce meaningful results and is likely a bug.

This error is reported by phpstan/phpstan-strict-rules.

How to fix it

Convert the value to an appropriate numeric type before decrementing, or use explicit arithmetic:

 <?php declare(strict_types = 1);

-function doFoo(string $s): void
+function doFoo(int $count): void
 {
-	--$s;
+	--$count;
 }