Error Identifier: possiblyImpure.propertyHookCall

← Back to possiblyImpure.*

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 Config
{
	private int $backing = 1;

	public int $counter {
		get {
			return $this->backing;
		}
	}
}

final class Service
{
	/** @phpstan-pure */
	public function read(Config $config): int
	{
		return $config->counter;
	}
}

Why is it reported? #

A function or method marked as @phpstan-pure accesses a property whose hook (PHP 8.4+) has an unknown purity. PHPStan cannot prove the hook is free of side effects, so it cannot guarantee that reading or writing the property is a pure operation.

A pure function must not have any side effects and must always return the same result for the same inputs. Related identifiers: impure.propertyHookCall is reported when the hook is known to be impure, possiblyImpure.methodCall covers the same situation for regular method calls.

How to fix it #

Mark the hook as @phpstan-pure so PHPStan knows it is safe to access from a pure context:

 public int $counter {
+	/** @phpstan-pure */
 	get {
 		return $this->backing;
 	}
 }

Or remove the @phpstan-pure annotation from the accessing method if it does not need to be pure:

-/** @phpstan-pure */
 public function read(Config $config): int
 {
 	return $config->counter;
 }

How to ignore this error #

You can use the identifier possiblyImpure.propertyHookCall to ignore this error using a comment:

// @phpstan-ignore possiblyImpure.propertyHookCall
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: possiblyImpure.propertyHookCall

Rules that report this error #

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