Error Identifier: pow.leftNonNumeric

Every error reported by PHPStan has an error identifier. Here’s a list of all error identifiers. In PHPStan Pro you can see the error identifier next to each error and filter errors by their identifiers.

Code example #

<?php declare(strict_types = 1);

function doFoo(): void
{
	$null = null;
	$result = $null ** 2;
}

Why is it reported? #

The exponentiation operator (**) is intended for numeric arithmetic. When a non-numeric value such as null, an object, or a non-numeric string is used on the left side of the ** operator, PHP will attempt implicit type coercion, which is error-prone and usually indicates a bug.

In the example above, null is used as the base of the exponentiation, which PHP silently coerces to 0.

This rule is provided by the phpstan-strict-rules package.

How to fix it #

Ensure the left operand is a numeric type (int, float, or numeric string):

 <?php declare(strict_types = 1);
 
-function doFoo(): void
+function doFoo(int $base): void
 {
-	$null = null;
-	$result = $null ** 2;
+	$result = $base ** 2;
 }

Or handle the possibly-null value explicitly:

 <?php declare(strict_types = 1);
 
 function doFoo(?int $base): void
 {
-	$result = $base ** 2;
+	$result = ($base ?? 0) ** 2;
 }

How to ignore this error #

You can use the identifier pow.leftNonNumeric to ignore this error using a comment:

// @phpstan-ignore pow.leftNonNumeric
codeThatProducesTheError();

You can also use only the identifier key to ignore all errors of the same type in your configuration file in the ignoreErrors parameter:

parameters:
	ignoreErrors:
		-
			identifier: pow.leftNonNumeric

Rules that report this error #

PHPStan\Rules\Operators\OperandsInArithmeticExponentiationRule [1] phpstan/phpstan-strict-rules

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