unaryMinus.nonNumeric

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

Code example

<?php declare(strict_types = 1);

function doFoo(?int $value): void
{
	$result = -$value;
}

Why is it reported?

The unary minus operator (-) is applied to a non-numeric value. In PHP, applying unary minus to non-numeric types like null, bool, string, array, or object produces unexpected results or errors. This rule enforces that only numeric types (int, float, or their union types) are used with the unary minus operator.

In the example above, $value has type int|null, and applying - to null is not a valid numeric operation.

How to fix it

Ensure the operand is a numeric type before applying unary minus:

 <?php declare(strict_types = 1);

 function doFoo(?int $value): void
 {
+	if ($value === null) {
+		return;
+	}
+
 	$result = -$value;
 }

Or change the parameter type to exclude non-numeric types:

 <?php declare(strict_types = 1);

-function doFoo(?int $value): void
+function doFoo(int $value): void
 {
 	$result = -$value;
 }