Error Identifier: pureFunction.nonOptionalParameterPassed

← Back to pureFunction.*

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);

/**
 * @param-out int $count
 * @pure-unless-parameter-passed $count
 */
function myReplace(string $subject, int &$count): string // ERROR: Function myReplace() is marked @pure-unless-parameter-passed for parameter $count, but $count is not optional, so function myReplace() is never pure.
{
	$count = 1;

	return $subject;
}

Why is it reported? #

The @pure-unless-parameter-passed tag marks a function as pure unless an argument is passed for the named by-reference parameter. It describes functions like preg_replace() or str_replace(), whose optional $count out-parameter is the only thing that makes a call impure: calls that omit it are pure, calls that pass it write into the caller’s variable.

Here $count has no default value, so every call has to pass it. The condition under which the function would be pure can never be met, which makes the tag meaningless — the function is effectively always impure.

How to fix it #

Make the parameter optional by giving it a default value, so callers can omit it and get a pure call:

 /**
  * @param-out int $count
  * @pure-unless-parameter-passed $count
  */
-function myReplace(string $subject, int &$count): string
+function myReplace(string $subject, int &$count = 0): string
 {
 	$count = 1;

 	return $subject;
 }

If the parameter has to stay required, the function is never pure. Remove the tag:

 /**
  * @param-out int $count
- * @pure-unless-parameter-passed $count
  */
 function myReplace(string $subject, int &$count): string

How to ignore this error #

You can use the identifier pureFunction.nonOptionalParameterPassed to ignore this error using a comment:

// @phpstan-ignore pureFunction.nonOptionalParameterPassed
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: pureFunction.nonOptionalParameterPassed

Rules that report this error #

• PHPStan\Rules\Pure\PureFunctionRule [1]
• PHPStan\Rules\Pure\PureMethodRule [1]
• PHPStan\Rules\Pure\PurePropertyHookRule [1]