generics.interfaceConflict

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.