There are multiple typehints in PHP, more now in PHP 8, and even more with Psalm. But what about declaring the type, rather than hinting the expected type?
I have a interface Collection extends Traversable, and I need to declare that it is a traversable of type Abc. How can I do that, so that PHPDoc or Psalm know that when I iterate over instances of my Collection, each element will be of type Abc?
In other words, I need to, on interface level, guarantee that the assertion will always pass:
function doWithItems(Collection $items): void
{
foreach ($items as $item) {
assert($item instanceof Abc);
}
}
I don't have a working interface example in my code (and these can be tricky to get right), but since Psalm implements interface Traversable<TKey, TValue> template on Traversable it would be something like:
/**
* @extends Traversable<array-key,Abc>
*/
interface Collection extends Traversable
A definitely working class-level example from my code using Doctrine Collections (which has very thorough Psalm support, you can look through source for how they do it):
/**
* @extends ArrayCollection<array-key, ShowInterface>
*/
final class Shows extends ArrayCollection