Re: [RFC] Interface Default Methods

On Thu, Jun 15, 2023 at 12:22 AM Juliette Reinders Folmer <php-internals_nospam@adviesenzo.nl> wrote: > > On 15-6-2023 5:47, Levi Morrison via internals wrote: > > I am moving my RFC for interface default methods to discussion: > > https://wiki.php.net/rfc/interface-default-methods. > > There are two things I'm missing on an initial read of the RFC. > > > Adding a default implementation to an existing interface method will > not break existing code, because every existing usage has a higher > priority than the default. > > A: How would this work if the existing method in the implementing class > has a different function signature than the newly introduced method in > the interface ? > There are two aspects to this: > 1. What if the existing method has different parameters ? > 2. What if the existing method has the same parameters, but > different/incompatible parameter/return types ? You mis-interpreted what I was trying to say, so I'll try to clarify that first, and then secondly address your question. If there an existing interface, say: interface Interface1 { function method1(); } The RFC is saying that if you added a default implementation to method1 without changing its signature at all, then that would not be a compatibility issue. All existing implementers have somehow implemented this method already, so adding a default will do nothing (it will be unused). As to your questions about incompatible signatures, it's not any different from any other interface method. If you add a new method to the interface, and it's not compatible with some existing method on an implementer, then it's a compatibility issue. That's not changing with default methods. What is changing is that if a new method is added to an interface, and it has a default implementation, it's way less likely to be a compatibility break, because we only have to worry about methods that share the same name. Without default methods, essentially all additions would be compatibility break. > B: How does the ability to add default method implementations to an > interface compare to providing an abstract class implementing the > interface and providing the default method implementations ? A key difference is that you can implement many interfaces, but can only extend a single class (abstract or not). For this reason, many contracts are formed with interfaces and relatively fewer with abstract classes. Well, that's my experience, anyway.