> I don't talk about "overhead". There is a clear subset relation, Natural <= > int so you know the conversion from Natural to int cannot fail.
Weren't we talking about subtracting with going down under zero? This can fail. I just want to understand how int subrange is a better solution than using checked uints (i.e. for indexing). > Well the example is simply about iterating over a subset if such a subset > exists Well, you see, you can't infer this _if_ clause you have from reading the code. This is, as it happens, just what it does, but it's not clear if this had been the intent of the one who wrote it. I have a hunch a panic on `for a in 0..-4` would be not a bad thing to do, because this expression doesn't make any sense, follows it's a bug. If it was some `0..<a.len().saturated_sub(4)` then both the intent and the behaviour would be absolutely unambiguously clear. On the other hand, this is just forcing proper code documenting with runtime costs, which is also not good. :P
