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Error Identifier: impure.methodCall

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
	{
		echo $message;
	}
}

class Calculator
{
	private Logger $logger;

	/** @phpstan-pure */
	public function add(int $a, int $b): int
	{
		$this->logger->log('adding');
		return $a + $b;
	}
}

Why is it reported? #

A function or method marked as @phpstan-pure must not cause any side effects. Calling an impure method (one that performs I/O, modifies external state, or is marked @phpstan-impure) inside a pure function violates purity guarantees. Pure functions must only depend on their arguments and return a value without observable side effects.

How to fix it #

Remove the impure method call from the pure function:

 /** @phpstan-pure */
 public function add(int $a, int $b): int
 {
-	$this->logger->log('adding');
 	return $a + $b;
 }

Or, if the side effect is intentional, remove the @phpstan-pure annotation:

-/** @phpstan-pure */
 public function add(int $a, int $b): int
 {
 	$this->logger->log('adding');
 	return $a + $b;
 }

How to ignore this error #

You can use the identifier impure.methodCall to ignore this error using a comment:

// @phpstan-ignore impure.methodCall
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: impure.methodCall

Rules that report this error #

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

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