Error Identifier: preDec.type

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);

$obj = new stdClass();
--$obj;

$arr = [];
--$arr;

Why is it reported? #

The pre-decrement operator (--) can only be used on variables of type int, float, string (numeric strings only), or null. Using it on other types such as objects, arrays, booleans, or resources is not a valid operation and may lead to unexpected behaviour or deprecation notices in newer PHP versions.

How to fix it #

Ensure the variable is of a type that supports the decrement operator. If the value is supposed to be a number, assign or cast it to the correct type first:

 <?php declare(strict_types = 1);
 
-$value = new stdClass();
---$value;
+$value = 1;
+--$value;

If the variable is a string that should be decremented, use str_decrement() (PHP 8.3+) instead:

 <?php declare(strict_types = 1);
 
 $str = 'b';
---$str;
+$str = str_decrement($str);

How to ignore this error #

You can use the identifier preDec.type to ignore this error using a comment:

// @phpstan-ignore preDec.type
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: preDec.type

Rules that report this error #

PHPStan\Rules\Operators\InvalidIncDecOperationRule [1]

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