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Subject: Re: [PHP-DEV] RFC: Trait expects interface
From: rowan.collins@gmail.com (Rowan Tommins)

On 06/01/2022 23:53, Robert Korulczyk wrote:
> But there is no easy way to say "`FooTrait::someMethod()` is 
> implementation of `FooInterface::someMethod()`" that PHP and SCA will 
> understand. And I think this proposal handles this quite well


I'm not convinced it does, actually. Consider the following trait:

trait PropertyCount {
     public function count(): int {
         return count(get_object_vars($this));
     }
}

This trait CAN be used to implement the built-in Countable interface, 
and it might be useful to label it as such; but does it really make 
sense to say that classes MUST implement that interface?

Even if we put it as a requirement, we can't guarantee that the class 
will actually use the trait's implementation of the interface, because 
this would still be valid:

class Foo implements Countable {
     private $whatever;

     use PropertyCount {
         count as getPropertyCount;
     }

     public function count(): int {
         return 0;
     }
}


It feels like this use case would work better with an annotation like 
/** @can-implement Countable */ since it is really just documentation 
about possible uses.

Regards,

-- 
Rowan Tommins
[IMSoP]