Is it possible to somehow extract implementation of sealed classes to separate files and still use `...

# language-evolution

[zokipirlo]

Is it possible to somehow extract implementation of sealed classes to separate files and still use SealedClass.InnerClass syntax?

For example:

sealed class Message(val...) {
    class Text(...) : Message(...) {
        ...    
    }
    class Image(...) : Message(...) {
        ...    
    }
}

when (message) {
    is Message.Text -> ...
    is Message.Image -> ...
}
fun someFun(val msg: Message.Text) {}

But if I extract Text and Image to separete file from Message class file, because that file can be easiliy thounds of lines of code long, it would become:

when (message) {
    is Text -> ...
    is Image -> ...
}

fun someFun(val msg: Text) {}

And when using those classes all around a project you lose hierarchy that Text is part of Message. I think it's still more pretty to use Message.Text . Could be possible somehow to combine best of both worlds?

[hfhbd]

You could use an internal extension function instead.

[zokipirlo]

How do you mean that?

[Wesley Hartford]

I think @zokipirlo wants to be able to define the subclasses of a sealed class across several files, which is possible, but also keep them as nested classes of the parent (Message in the example case). Is that right?

I don't think that's currently possible, but in theory I like the idea. In a lot of cases, it makes sense to use a sealed child class with a qualified syntax such as Message.Text, but if there are a whole lot of sub-classes, the file declaring them all could get unpleasantly large.

[zokipirlo]

Yes, exactly that @Wesley Hartford

[zokipirlo]

Something like C# partial class maybe. Define all of them in sealed class but implement them in separate file.

[stantronic]

I would like to see a broader concept of extension classes - so you could define any class as class Parent.Child()