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kotlinlang

Why are non-tail-recursive functions marked with `tailrec` only a warning and not an error?

Because the tail recursion can still apply to the valid tail calls.

So if there are 3 returns, and 2 are tailrec, the function will be able to tailrec on these two?

Thanks! I didn't know that was possible, interesting

Then, why isn't it an error when *no* return is tailrec?

Yeah I'm also wondering. Whether the tail recursion can be unrolled is statically known at compile time, so the compiler should be able to tell when `tailrec` doesn't apply at all. It could be an error, then

I'm not sure if `tailrec` affects the calling ABI on any platform… on JVM it doesn't, but if it did, then that would be a reason to allow no-op `tailrec`, so that a function that was formerly `tailrec` and changed implementation would not be broken. (the other way around could be handled with a wrapper function)

it does feel like it should at least be a warning though