Re: Optional interfaces

On Sat, Nov 16, 2024, at 12:43, Valentin Udaltsov wrote: > On Sat, 16 November 2024 at 13:42 Rob Landers <rob@bottled.codes> wrote: >> __ >> On Sat, Nov 16, 2024, at 10:02, Juris Evertovskis wrote: >>> Is there some reason you cannot do this: >>> >>> https://3v4l.org/hF1vr >>> >>> Unless I’m missing something, you can’t patch-define a namespaced OptionalInterface >>> that easily. >>> >>> Anyway, I was not implying this is something impossible to accomplish. My point is that >>> it would be beneficial to have syntax for expressing “if your app has this interface, our class >>> implements it”. >>> >>> Juris >> >> Yeah, I get it now (see my reply to Marco). >> >> Even with namespaces, it is pretty straightforward, though: >> https://3v4l.org/dmXoB >> >> — Rob > > This is a nice solution. > > However, interface_exists should be used for interfaces. > > -- > Valentin >> Actually, you'd probably want to check for both (as well as traits) for a better developer experience. For example, using interface_exists results in the error "Cannot declare interface, because the name is already in use" if a class with the same name is used instead of an interface. This is a nonsensical error message because the library is not responsible for declaring it. Instead, you'd want the error message to be more actionable: "cannot implement class -- it is not an interface" — Rob