Yes, you are right, I didn't consider the checkcast instruction.
Yes, F# does not have this particular limitation, but has few of its own in different places. Most notably, it lacks HKT (arguably, because of CLR awareness of generics).
BTW, alternative approaches to stack-safe recursion do exist in Scala. For example, https://github.com/slamdata/matryoshka
And guess what? it doesn't have it because F# doesn't run on the JVM! If it run in the JVM, it would have it. So your obsession with "runtime" as a platform not only not useful, it's asking for trouble! ;)
@tailrec is not necessary to enable tailcalls.
All the annotation does is error if a function is not able to be optimized for tail calls.
The (attempt at) optimization takes place either way, you don't need the annotation unless there's some doubt in your mind.
> As for regular objects, no casts are needed.
Are you sure? See https://stackoverflow.com/a/10126425/544947
> Hardly a "horror story".
F# doesn't have this limitation and F# does tailcalls by default instead of having to explicitly remember to decorate it with the @tailrec attribute.