In my compilers class, this is how we did static downcasting for the toy language we created (I think it was called Oat?). I think it's clever, but I find that I prefer mechanisms that rebind the variable for clarity purposes. It's super easy IMO to accidentally gloss over something as being just a regular if statement rather than something that's actually statically changing the type of the variable compared to having different syntax than just a regular conditional. I also tend to prefer being able to look at a variable's usage and then look back to the time it was initialized and know that it's still the same type; having the type change only within a given scope without any explicit binding seems like something I'd mess up a lot, especially when reviewing code I didn't write myself.