Error Identifier: pureMethod.parameterPassedNotByRef

← Back to pureMethod.*

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);

class Replacer
{

	/**
	 * @pure-unless-parameter-passed $flag
	 */
	public function replaceByValue(string $subject, bool $flag = false): string // ERROR: Method Replacer::replaceByValue() is marked @pure-unless-parameter-passed for parameter $flag, but $flag is not passed by reference.
	{
		return $subject;
	}

}

Why is it reported? #

The @pure-unless-parameter-passed tag marks a method as pure unless an argument is passed for the named parameter. It is meant for optional by-reference out-parameters: writing into the caller’s variable through such a parameter is the side effect that makes the call impure.

A parameter passed by value cannot produce a side effect just by being passed — the method only receives a copy. The tag therefore has no meaning on a by-value parameter. This mirrors pureFunction.parameterPassedNotByRef for functions.

How to fix it #

If the method has no side effects, mark it as pure instead:

 	/**
-	 * @pure-unless-parameter-passed $flag
+	 * @phpstan-pure
 	 */
 	public function replaceByValue(string $subject, bool $flag = false): string

If the parameter is meant to be an out-parameter, declare it by reference and describe the written type with @param-out:

 	/**
+	 * @param-out int $count
-	 * @pure-unless-parameter-passed $flag
+	 * @pure-unless-parameter-passed $count
 	 */
-	public function replaceByValue(string $subject, bool $flag = false): string
+	public function replace(string $subject, int &$count = 0): string
 	{
+		$count = 1;
+
 		return $subject;
 	}

How to ignore this error #

You can use the identifier pureMethod.parameterPassedNotByRef to ignore this error using a comment:

// @phpstan-ignore pureMethod.parameterPassedNotByRef
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: pureMethod.parameterPassedNotByRef

Rules that report this error #

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