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Error Identifier: impureFunction.pure

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 Logger
{
	/** @phpstan-impure */
	public function log(string $message): void
	{
		file_put_contents('/var/log/app.log', $message);
	}
}

class Calculator
{
	/** @phpstan-impure */
	public function add(int $a, int $b): int
	{
		return $a + $b;
	}
}

Why is it reported? #

A function or method is marked as impure (via the @phpstan-impure PHPDoc tag) but does not contain any actual side effects. PHPStan detects that the function has no impure points such as I/O operations, property assignments, global state access, or calls to other impure functions. If a function truly has no side effects, it should not be marked as impure.

How to fix it #

If the function genuinely has no side effects, remove the @phpstan-impure annotation. Optionally mark it as @phpstan-pure instead.

 <?php declare(strict_types = 1);
 
 class Calculator
 {
-	/** @phpstan-impure */
+	/** @phpstan-pure */
 	public function add(int $a, int $b): int
 	{
 		return $a + $b;
 	}
 }

How to ignore this error #

You can use the identifier impureFunction.pure to ignore this error using a comment:

// @phpstan-ignore impureFunction.pure
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: impureFunction.pure

Rules that report this error #

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

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