Hello. I have a class (let's call it `Entity`) tha...

# announcements

[Benoit Duffez]

Hello.
I have a class (let's call it Entity) that is inherited from two children, and they need to change the type of one property.

This is because these classes are used to retrieve data from a backend (in serialized in JSON, deserialized with Gson). In fact, the server uses the same object for downlink (e.g. GET /x/y/z.json returns a list of Entity) and uplink (POST /abc with one Entity in the body), but one of the fields has not the same type whether it's uplink or downlink (bummer... I can't change the server code...).

So in Entity i have declared the property as open var stuff: Any? = null, and I expected the EntityUplink for example to have override var stuff: ActualType? = null but the compiler refuses that.

Is that a violation of the language (e.g. not possible/not designed to do that) or am I missing something?

[hho]

Well, that's a consequence of the https://en.wikipedia.org/wiki/Liskov_substitution_principle

If you have a class that deals with Entity objects, it expects to be able to put Any type in the stuff field. You can't have a subclass which restricts that.

[Benoit Duffez]

Thanks a lot. Didn't know this WP article.

[Benoit Duffez]

Actually the subclass doesn't restrict that, it's just that this field is retrieved from the local database, and my abstraction layer needs an explicit type to figure out how to convert from database type to kotlin type.

[Benoit Duffez]

it could deal with Any but then I would need a workaround in the database code so that the DAO knows how to extract this Any from the database.

[Benoit Duffez]

anyway this is no longer relevant, see main channel.