Error Identifier: generics.interfaceConflict

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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);

class Item {}

/**
 * @extends \Traversable<int, Item>
 */
interface ItemListInterface extends \Traversable
{
}

/**
 * @implements \IteratorAggregate<int, string>
 */
final class ItemList implements \IteratorAggregate, ItemListInterface
{
	public function getIterator(): \Traversable
	{
		return new \ArrayIterator([]);
	}
}

Why is it reported? #

A class or interface specifies conflicting type arguments for the same generic interface through different inheritance paths. When a class implements or extends the same generic interface multiple times (through different parent interfaces or classes), the template type arguments must be identical.

In the example above, ItemList implements IteratorAggregate<int, string> and ItemListInterface which extends Traversable<int, Item>. Since IteratorAggregate also extends Traversable, the class inherits Traversable twice – once with TValue as string (from IteratorAggregate) and once with TValue as Item (from ItemListInterface). This creates a conflict because the template type cannot be both string and Item.

How to fix it #

Ensure all inheritance paths specify the same type arguments for the shared interface:

 /**
- * @implements \IteratorAggregate<int, string>
+ * @implements \IteratorAggregate<int, Item>
  */
 final class ItemList implements \IteratorAggregate, ItemListInterface
 {
 	public function getIterator(): \Traversable
 	{
 		return new \ArrayIterator([]);
 	}
 }

Or restructure the class hierarchy to avoid implementing the same generic interface with different type arguments.

How to ignore this error #

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

// @phpstan-ignore generics.interfaceConflict
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.interfaceConflict

Rules that report this error #

• PHPStan\Rules\Generics\ClassAncestorsRule [1]
• PHPStan\Rules\Generics\EnumAncestorsRule [1]
• PHPStan\Rules\Generics\InterfaceAncestorsRule [1]