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Error Identifier: generics.traitBound

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
{
}

/**
 * @template T of MyTrait
 */
class Collection // error: invalid bound type MyTrait
{
}

Why is it reported? #

A @template tag uses a trait as its bound type or default type. Traits cannot be used as type bounds because they are not standalone types in PHP’s type system – they cannot be used in type declarations, instanceof checks, or as parameter/return types. A template type bound must be a class, interface, or a built-in type.

This applies to @template tags on classes, interfaces, traits, functions, and methods.

How to fix it #

Replace the trait with an interface or a class as the bound type:

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

 /**
- * @template T of MyTrait
+ * @template T of MyInterface
  */
 class Collection
 {
 }

If you need to constrain the template type to classes that use a specific trait, consider extracting an interface that the trait’s users implement:

<?php declare(strict_types = 1);

interface Loggable
{
	public function log(string $message): void;
}

trait LoggableTrait
{
	public function log(string $message): void
	{
		// ...
	}
}

/**
 * @template T of Loggable
 */
class Collection
{
}

How to ignore this error #

You can use the identifier generics.traitBound to ignore this error using a comment:

// @phpstan-ignore generics.traitBound
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: generics.traitBound

Rules that report this error #

• PHPStan\Rules\Generics\ClassTemplateTypeRule [1] [2]
• PHPStan\Rules\Generics\FunctionTemplateTypeRule [1] [2]
• PHPStan\Rules\Generics\InterfaceTemplateTypeRule [1] [2]
• PHPStan\Rules\Generics\MethodTagTemplateTypeRule [1] [2]
• PHPStan\Rules\Generics\MethodTagTemplateTypeTraitRule [1] [2]
• PHPStan\Rules\Generics\MethodTemplateTypeRule [1] [2]
• PHPStan\Rules\Generics\TraitTemplateTypeRule [1] [2]
• PHPStan\Rules\PhpDoc\IncompatiblePhpDocTypeRule [1] [2]
• PHPStan\Rules\PhpDoc\IncompatiblePropertyHookPhpDocTypeRule [1] [2]
• PHPStan\Rules\PhpDoc\IncompatiblePropertyPhpDocTypeRule [1] [2]

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