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Error Identifier: possiblyImpure.propertyAssignByRef

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 $value = 0;

	/**
	 * @phpstan-pure
	 */
	public function getRef(): int
	{
		$ref = &$this->value;

		return 1;
	}
}

Why is it reported? #

The function or method is marked as @phpstan-pure but creates a reference to a property via &$this->property or &$object->property. Assigning by reference to a property is a potential side effect because modifying the reference variable later would also modify the property. Pure functions must not have side effects.

How to fix it #

Remove the by-reference assignment, or remove the @phpstan-pure annotation:

 /**
- * @phpstan-pure
  */
 public function getRef(): int
 {
-	$ref = &$this->value;
+	$ref = $this->value;

 	return 1;
 }

How to ignore this error #

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

// @phpstan-ignore possiblyImpure.propertyAssignByRef
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.propertyAssignByRef

Rules that report this error #

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

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