Can you override interface methods with different, but “compatible”, signatures?

Question

Consider the following PHP interfaces:

interface Item {
    // some methods here
}

interface SuperItem extends Item {
    // some extra methods here, not define         


        

Answer 1

Extending interface is not allowed to change method definitions. If your SuperItem is extending Item, it should be passing through classes implementing Collection interface without problems.

But based on what you really want to do, you can try:

• Create interface with slightly different methods for SuperItem and implement that:

  interface SuperCollection extends Collection {
      public function addSuper(SuperItem $superItem);
  }
  

• Use decorator pattern to create almost same interface without extending:

  interface Collection {
      public function add(Item $item);
      // more methods here
  }
  
  interface SuperCollection {
      public function add(SuperItem $item);
      // more methods here that "override" the Collection methods like "add()" does
  }
  

  Then decorator (abstract) class, which will use this interface:

  class BasicCollection implements Collection {
      public function add(Item $item)
      {
      }
  }
  
  class DecoratingBasicCollection implements SuperCollection {
      protected $collection;
  
      public function __construct(Collection $collection)
      {
          $this->collection = $collection;
      }
  
      public function add(SuperItem $item)
      {
          $this->collection->add($item);
      }
  }