Re: [RFC] [Initial Feedback] Abstract class constants

Hi John, On 8/15/26 11:53 PM, John Bafford wrote: > I like this idea, and along those lines, I would suggest that > interfaces could also benefit from this. > > Currently, you can write something like: > > ``` > interface I { > public int $x { get; } > } > > abstract class C implements I {} > > class CC extends C {} > ``` > > //Fatal error: Class CC contains 1 abstract method and must therefore > be declared abstract or implement the remaining method (I::$x::get) in > /in/U49c0 on line 9 > > > The abstract class C does not by itself meet the requirements of the > interface I, but that's okay, because it's abstract. Conformance is > required by its concrete subclasses (which in this case errors because > it's missing). > > What's missing is for interfaces to be able to have static property > requirements (and constants, and readonly also). So we could fill in a > gap with interfaces as well. I initially didn't contemplate support for abstract class constants for interfaces as I hadn't encountered a situation where having it on an interface would be better than on a base class or trait. Now that you have brought it up I can envision an interface FieldChecker with a constant MESSAGE that would expected to be there. In this case it's the fact that the message is accessible statically, rather than it being able to be accessed by a method, that makes it useful. Given that this RFC proposal would add support for class constant declaration, I don't see a problem on adding constants to interfaces. In this case, class constant declaration would look something like: ```PHP interface I { public const string CONSTANT_NAME; ... } abstract class C { abstract public const string CONSTANT_NAME; ... } trait T { abstract public const string CONSTANT_NAME; ... } ``` What I do find rather curious is that interfaces don't already have any support for static properties. Is there a reason for this? If no one opposes, I'll be include support for class constant declaration in interfaces to the RFC. That said, I'd appreciate to have more feedback from the rest of the internals. Thank you for yours. Sincerely, Eloi Montañés.