This means you can't use interfaces as tags, which is a very important feature (e.g. see how it's used in Rust). It also means that you have several different t

This means you can't use interfaces as tags, which is a very important feature (e.g. see how it's used in Rust). It also means that you have several different types implementing your interface "by coincidence", making it difficult to use an IDE to find out the types of interest, not to mention what sorts of bugs might result because of this. There are better solutions like what Kotlin and Scala use (and potentially C# in a future version).