Error Identifier: property.readOnlyByPhpDocAssignByRef

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
{
	/**
	 * @var int
	 * @readonly
	 */
	public $value;

	public function __construct(int $value)
	{
		$this->value = $value;
	}

	public function doFoo(): void
	{
		$ref = &$this->value; // ERROR: @readonly property Foo::$value is assigned by reference.
	}
}

Why is it reported? #

A property marked with the @readonly PHPDoc annotation is being assigned by reference. When a variable holds a reference to a property, the property’s value can be changed through that reference, which violates the @readonly contract. Even if the code does not intend to modify the property through the reference, the reference itself creates a pathway for mutation.

How to fix it #

Read the property value into a regular variable instead of creating a reference:

 <?php declare(strict_types = 1);
 
 class Foo
 {
 	public function doFoo(): void
 	{
-		$ref = &$this->value;
+		$ref = $this->value;
 	}
 }

If the property should actually be mutable, remove the @readonly annotation:

 <?php declare(strict_types = 1);
 
 class Foo
 {
 	/**
 	 * @var int
-	 * @readonly
 	 */
 	public $value;
 }

How to ignore this error #

You can use the identifier property.readOnlyByPhpDocAssignByRef to ignore this error using a comment:

// @phpstan-ignore property.readOnlyByPhpDocAssignByRef
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: property.readOnlyByPhpDocAssignByRef

Rules that report this error #

PHPStan\Rules\Properties\ReadOnlyByPhpDocPropertyAssignRefRule [1]

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