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Error Identifier: impure.propertyAssign

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 Counter
{
	public int $count = 0;

	/** @phpstan-pure */
	public function increment(): int
	{
		$this->count++;
		return $this->count;
	}
}

Why is it reported? #

A function or method marked as @phpstan-pure contains a property assignment. Pure functions must not have side effects, and modifying an object’s property is a side effect because it changes the observable state.

How to fix it #

Remove the property assignment from the pure function:

 <?php declare(strict_types = 1);
 
 class Counter
 {
 	public int $count = 0;

-	/** @phpstan-pure */
-	public function increment(): int
+	public function increment(): int
 	{
 		$this->count++;
 		return $this->count;
 	}
 }

Or restructure the code so the pure function does not mutate state.

How to ignore this error #

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

// @phpstan-ignore impure.propertyAssign
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.propertyAssign

Rules that report this error #

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

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