One day I really ought to write an elaborate love letter blog post for #kotlinlang's `sealed interface`. It's extremely powerful and I keep on finding new ways to use it to make our codebase leaner yet rock solid safe. Differentiate only where relevant, otherwise share code where possible. Subtype it to restrict if you need. Litter in decorating interfaces to apply behaviour or externally derived properties as needed, ... I could go on. Hence the need for a blog post.