Error Identifier: impureMethod.pure

← Back to impureMethod.*

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);

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

Why is it reported? #

A method is marked as @phpstan-impure but PHPStan’s analysis found no actual side effects in its body. The method does not perform I/O, modify external state, or call other impure code. Marking a side-effect-free method as impure is misleading – callers cannot benefit from purity optimizations, and the annotation does not match the actual behavior.

This is only reported for methods that cannot be overridden – either in a final class, or when the method itself is final. For non-final methods, a subclass might introduce side effects, so PHPStan does not report this.

How to fix it #

Remove the @phpstan-impure annotation since the method has no side effects:

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

Or simply remove the annotation entirely and let PHPStan infer purity:

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

How to ignore this error #

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

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

Rules that report this error #

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