PHP type-hinting traits

Question

I have a trait. For the sake of creativity, let's call this trait Trait:

trait Trait{    
    static function treat($instance){    
        // treat that trait instance with care
    }
}

Now, I also have a class that uses this trait, User. When trying to call treat with an instance of User, everything works. But I would like to type-hint that only instances of classes using Trait should be given as arguments, like that:

static function treat(Trait $instance){...}

Sadly, though, this results in a fatal error that says the function was expecting an instance of Trait, but an instance of User was given. That type of type-hinting works perfectly for inheritance and implementation, but how do I type-hint a trait?

Answer 1

You can't as DaveRandom says. And you shouldn't. You probably want to implement an interface and typehint on that. You can then implement that interface using a trait.

Answer 2

For people ending up here in the future, I would like to elaborate on Veda's answer.

1. It's true that you can't treat traits as traits in PHP (ironically), saying that you expect an object that has some traits is only possible via interfaces (essentially a collection of abstract traits)
2. Other languages (such as Rust) actually encourage type hinting with traits

In conclusion; your idea is not a crazy one! It actually makes a lot of sense to view traits as what they are in the common sense of the word, and other languages do this. PHP seems to be stuck in the middle between interfaces and traits for some reason.