Error Identifier: preInc.nonNumeric

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.

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

Code example #

<?php declare(strict_types = 1);

function next(string $letter): string
{
	return ++$letter;
}

Why is it reported? #

The ++ (pre-increment) operator is being used on a value that is not numeric. While PHP allows incrementing strings (e.g., 'a' becomes 'b'), this behaviour can be surprising and error-prone. The strict rules require that only numeric types (int or float) are used with the increment operator to prevent unintended results.

How to fix it #

Use an explicit operation that makes the intent clear:

 <?php declare(strict_types = 1);
 
 function next(string $letter): string
 {
-	return ++$letter;
+	return chr(ord($letter) + 1);
 }

Or ensure the variable is typed as int if you intend numeric increment:

 <?php declare(strict_types = 1);
 
-function next(string $letter): string
+function next(int $counter): int
 {
-	return ++$letter;
+	return ++$counter;
 }

How to ignore this error #

You can use the identifier preInc.nonNumeric to ignore this error using a comment:

// @phpstan-ignore preInc.nonNumeric
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: preInc.nonNumeric

Rules that report this error #

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

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