Error Identifier: property.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
{
}

class Foo
{
	public MyTrait $bar; // ERROR: Property Foo::$bar has invalid type MyTrait.
}

Why is it reported? #

A trait is being used as a type for a class property. In PHP, traits are not types – they are a mechanism for horizontal code reuse. A trait cannot be used as a type declaration for properties, parameters, or return types. Unlike classes and interfaces, traits do not define a type that objects can be checked against.

How to fix it #

Use an interface or class as the property type instead of a trait:

 <?php declare(strict_types = 1);
 
-trait MyTrait
+interface MyInterface
 {
 }

 class Foo
 {
-	public MyTrait $bar;
+	public MyInterface $bar;
 }

If the trait defines shared behavior, extract an interface that classes using the trait should implement:

 <?php declare(strict_types = 1);
 
+interface HasName
+{
+	public function getName(): string;
+}
+
 trait NameTrait
 {
 	public function getName(): string
 	{
 		return $this->name;
 	}
 }

 class Foo
 {
-	public NameTrait $entity;
+	public HasName $entity;
 }

How to ignore this error #

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

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

Rules that report this error #

PHPStan\Rules\Properties\ExistingClassesInPropertiesRule [1]

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