Error Identifier: impure.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 Foo
{
public int $value = 0;
/** @phpstan-pure */
public function doSomething(): int
{
$ref = &$this->value;
return 1;
}
}
Why is it reported? #
The method is declared as pure using @phpstan-pure, but it creates a reference to an object property ($ref = &$this->value). Assigning a variable by reference to a property is a possibly impure operation because modifying the reference variable later would mutate the object’s state, which violates the purity contract.
Pure functions and methods must not have side effects – they should only compute and return a value based on their inputs.
How to fix it #
If the method needs to reference object properties, remove the @phpstan-pure annotation:
- /** @phpstan-pure */
public function doSomething(): int
{
$ref = &$this->value;
return 1;
}
If the method should remain pure, avoid creating references to properties:
/** @phpstan-pure */
public function doSomething(): int
{
- $ref = &$this->value;
+ $ref = $this->value;
return 1;
}
How to ignore this error #
You can use the identifier impure.propertyAssignByRef to ignore this error using a comment:
// @phpstan-ignore impure.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: impure.propertyAssignByRef