Not super comfortable with sealed classes. I'm trying to model an action type that can model things like a phone button click, or a url click, or unhandled (unknown). How does this look?

sealed class GenericActionType {
    class Dialer(phoneUri: String) : GenericActionType()
    class Browser(url: String) : GenericActionType()
    object Unknown : GenericActionType()
}

The structure looks good to me, although I would probably use

data class

for the ones with data, it's often useful for printing/copying/equaling etc. Regarding naming, maybe avoid "generic" and "type" in the name: • "generic" is not advisable because nested child classes will look weird when referenced (they use the parent type):

GenericActionType.Dialer(...)

• "Type" doesn't seem appropriate here because this is already a type, and that type represents an action, not an action type. If it were an action type you wouldn't have data associated with it like those urls Maybe

Action.Dial

would look better

True. I guess I'm trying to not interfere with other classes called Action. Great feedback though. Thanks

Yeah I guess to avoid conflicts you might want to find a more precise name than

Action

but these "generic" and "type" words didn't give more precision IMO. Maybe some words from the domain would help, like

UserAction

or something

Also, tiny improvement, unless

GenericActionType

defines something for the subclasses, consider using

sealed interface

ooh. good point too @Luke

you kind of have to make at least one really good mess with sealed classes and way over-modeling a domain to get a feel for when they're the right tool 🙂

If you know about design patterns, this is what visitor pattern tries to do in a awkward way.