Error Identifier: parameterByRef.unusedType

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 doFoo(int|string &$value): void
{
	$value = 42;
}

Why is it reported? #

A by-reference parameter has a union type, but the function never assigns one of the union members to it. In the example above, $value is typed as int|string, but the function only ever assigns an int. The string part of the union is never used and can be removed.

How to fix it #

Narrow the type to only include what is actually assigned:

 <?php declare(strict_types = 1);
 
-function doFoo(int|string &$value): void
+function doFoo(int &$value): void
 {
 	$value = 42;
 }

You can also narrow the parameter out type with a @param-out PHPDoc tag if you cannot change the native type.

How to ignore this error #

You can use the identifier parameterByRef.unusedType to ignore this error using a comment:

// @phpstan-ignore parameterByRef.unusedType
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: parameterByRef.unusedType

Rules that report this error #

PHPStan\Rules\TooWideTypehints\TooWideArrowFunctionReturnTypehintRule [1]
PHPStan\Rules\TooWideTypehints\TooWideClosureReturnTypehintRule [1]
PHPStan\Rules\TooWideTypehints\TooWideFunctionParameterOutTypeRule [1]
PHPStan\Rules\TooWideTypehints\TooWideFunctionReturnTypehintRule [1]
PHPStan\Rules\TooWideTypehints\TooWideMethodParameterOutTypeRule [1]
PHPStan\Rules\TooWideTypehints\TooWideMethodReturnTypehintRule [1]
PHPStan\Rules\TooWideTypehints\TooWidePropertyTypeRule [1]

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