Error Identifier: paramOut.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);

/**
 * @param-out int|string $result
 */
function compute(mixed &$result): void
{
	$result = 42;
}

Why is it reported? #

The @param-out type annotation declares a union type for a by-reference parameter, but one of the types in the union is never actually assigned to the parameter. PHPStan analyzes all code paths in the function and determines that a part of the declared output type is too wide because it is never used. This indicates that the @param-out annotation is more permissive than what the function actually produces.

How to fix it #

Narrow the @param-out type to only include the types that are actually assigned to the parameter.

 <?php declare(strict_types = 1);
 
 /**
- * @param-out int|string $result
+ * @param-out int $result
  */
 function compute(mixed &$result): void
 {
 	$result = 42;
 }

How to ignore this error #

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

// @phpstan-ignore paramOut.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: paramOut.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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