Hey! Thanks, I'm glad that you found the article useful.

If I'm understanding your question properly, I think the answer would depend completely on the context of what you're doing. In some instances, it might be suitable to add method E to it's own separate interface that only class 1 could implement.

On the other hand, it might be easier to throw an exception in the other methods saying that the method is not implemented. I've seen this done before in some packages (and I think some parts of the File drivers in Laravel, but I might be wrong).

So, as I say, I think it would depend on what you were trying to solve and who was intending on using the code. If it's for a package that's going to be used publicly, you might want to approach it differently to if you were just building it as internal class that you're going to be using in your own projects.

Hopefully that helps a little bit?