Error Identifier: argument.byRef

← Back to argument.*

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);

function increment(int &$value): void
{
	$value++;
}

function doFoo(): void
{
	increment(rand());
}

Why is it reported? #

When a function parameter is declared with & (pass by reference), PHP requires the caller to pass a variable, array element, or property – something that can be written back to. Passing an expression such as a function call result, a literal, or a null is not valid because there is no storage location for PHP to write the modified value into. Similarly, a readonly or @readonly property cannot be passed by reference because it must not be modified after initialisation.

How to fix it #

Store the value in a variable before passing it by reference:

 <?php declare(strict_types = 1);
 
 function increment(int &$value): void
 {
 	$value++;
 }

 function doFoo(): void
 {
-	increment(rand());
+	$number = rand();
+	increment($number);
 }

Or, if the function does not actually need to modify the argument, remove the & from the parameter declaration:

 <?php declare(strict_types = 1);
 
-function increment(int &$value): void
+function increment(int $value): int
 {
-	$value++;
+	return $value + 1;
 }

How to ignore this error #

You can use the identifier argument.byRef to ignore this error using a comment:

// @phpstan-ignore argument.byRef
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: argument.byRef

Rules that report this error #

• PHPStan\Rules\Classes\ClassAttributesRule [1] [2] [3]
• PHPStan\Rules\Classes\ClassConstantAttributesRule [1] [2] [3]
• PHPStan\Rules\Classes\InstantiationRule [1] [2] [3]
• PHPStan\Rules\Constants\ConstantAttributesRule [1] [2] [3]
• PHPStan\Rules\EnumCases\EnumCaseAttributesRule [1] [2] [3]
• PHPStan\Rules\Functions\ArrowFunctionAttributesRule [1] [2] [3]
• PHPStan\Rules\Functions\CallCallablesRule [1] [2] [3]
• PHPStan\Rules\Functions\CallToFunctionParametersRule [1] [2] [3]
• PHPStan\Rules\Functions\CallUserFuncRule [1] [2] [3]
• PHPStan\Rules\Functions\ClosureAttributesRule [1] [2] [3]
• PHPStan\Rules\Functions\FunctionAttributesRule [1] [2] [3]
• PHPStan\Rules\Functions\ParamAttributesRule [1] [2] [3]
• PHPStan\Rules\Methods\CallMethodsRule [1] [2] [3]
• PHPStan\Rules\Methods\CallStaticMethodsRule [1] [2] [3]
• PHPStan\Rules\Methods\MethodAttributesRule [1] [2] [3]
• PHPStan\Rules\Properties\PropertyAttributesRule [1] [2] [3]
• PHPStan\Rules\Properties\PropertyHookAttributesRule [1] [2] [3]
• PHPStan\Rules\Traits\TraitAttributesRule [1] [2] [3]