Error Identifier: impure.propertyHookCall

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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 {
		/** @phpstan-impure */
		get {
			echo 'accessed';
			return $this->backing;
		}
	}
}

final class Service
{
	/** @phpstan-pure */
	public function read(Config $config): int
	{
		return $config->counter; // ERROR: Impure call to get hook of property Config::$counter in pure method Service::read().
	}
}

Why is it reported? #

A function or method marked as @phpstan-pure must not cause any side effects. Property hooks (PHP 8.4+) run code when a property is read or written, so accessing a property that has an impure hook effectively calls impure code.

In the example, reading $config->counter invokes the get hook, which is marked @phpstan-impure and performs I/O. Because the hook has side effects, reading the property is not a pure operation, and doing so from a pure method violates the purity contract.

How to fix it #

Remove the property access with the impure hook from the pure method:

 /** @phpstan-pure */
 public function read(Config $config): int
 {
-	return $config->counter;
+	return 0;
 }

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

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

If the hook does not actually have side effects, remove its @phpstan-impure annotation so PHPStan can treat the property access as pure:

 public int $counter {
-	/** @phpstan-impure */
 	get => $this->backing;
 }

How to ignore this error #

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

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

Rules that report this error #

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