To be clear, in this case if you don't want to think about it, and just want to use dynamic dispatch, you absolutely can! Just return a boxed iterator for the n

To be clear, in this case if you don't want to think about it, and just want to use dynamic dispatch, you absolutely can! Just return a boxed iterator for the normal case, and a boxed empty iterator for the special case. Rust's dynamic dispatch will basically mean they're both the `Box<impl Iterator<Item=T>>` type, which is actually implemented with an allocation and vtable. Everything will work fine. You can optimize it later if it actually matters. I've done this type of thing plenty of times when working on non-critical code where I just wanted to get something to quickly work without thinking about it too hard.