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Error Identifier: parameter.trait

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);

trait MyTrait
{
	public function doSomething(): void
	{
	}
}

function doFoo(MyTrait $param): void // error: Parameter $param of function doFoo() has invalid type MyTrait.
{
}

Why is it reported? #

Traits cannot be used as type declarations in PHP. Unlike classes and interfaces, traits are a code reuse mechanism and do not define a type that can be checked at runtime. Using a trait as a parameter type will cause a fatal error. PHP only allows classes, interfaces, and built-in types in parameter type declarations.

How to fix it #

Extract an interface from the trait and use it as the parameter type instead.

+interface MyTraitInterface
+{
+	public function doSomething(): void;
+}
+
 trait MyTrait
 {
 	public function doSomething(): void
 	{
 	}
 }

-function doFoo(MyTrait $param): void
+function doFoo(MyTraitInterface $param): void
 {
 }

How to ignore this error #

You can use the identifier parameter.trait to ignore this error using a comment:

// @phpstan-ignore parameter.trait
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: parameter.trait

Rules that report this error #

• PHPStan\Rules\Functions\ExistingClassesInArrowFunctionTypehintsRule [1] [2]
• PHPStan\Rules\Functions\ExistingClassesInClosureTypehintsRule [1] [2]
• PHPStan\Rules\Functions\ExistingClassesInTypehintsRule [1] [2]
• PHPStan\Rules\Methods\ExistingClassesInTypehintsRule [1] [2]
• PHPStan\Rules\Properties\ExistingClassesInPropertyHookTypehintsRule [1] [2]

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