This seems to be a language inconsistency.
let a = 5 let b = a++ b == 5 let a = 5 let b = ++a b == 6
This is a useful behavior. Why should only value-1 iterators enjoy it?
Here is a possible syntax for non-1 iterators. This syntax seems maybe good, because it's not an existing syntax. Currently, it would raise an error, so adding it to the language won't break anything. Also seems good because it's the same operator (++) as the value-1 pre/post operator.
// Pre: 5 ++a, or ++a 5 // Post: a++ 5
The following form shouldn't be used, because it's already in-use, and it's current behavior is (non-intuitively) prefix. Therefor, changing it to postfix would break existing code.
a += 5