'Double modulo' operator

[Jens]

@Adam_Nemecek

Seems like making it an operator will cause more issues than it solves. I think that floordiv and mod functions are probably the way to go. I'm going to wait a little longer for more feedback and write up a proposal at some point.

Sorry for bumping this thread after more than two years, but it's because of a recent related post and my concurrence with the people upthread who says essentially:

• I’ve never actually wanted a negative return value from %. It does what I need only as long as the lhs is positive, but not when it's negative. In fact, I wouldn't be surprised if many uses of % are in situations where only a positive lhs has been considered, and if the use case was generalized to work also for a negative lhs, the code wouldn't work as intended unless % is replaced with a "true modulo" operation.

• I've had to write a true mod function enough times across different projects (circular buffer indexing, angular arithmetic, periodic boundary conditions, subdivision of coordinate grids in games or graphics apps, etc.) that I would absolutely support its inclusion in the Standard Library.

I also think that this thread has arrived at some important conclusions (especially the ones quoted above), so it seems better to continue this discussion here rather than in a new thread. And there might be one more thing that needs to be sorted out before a proposal:

@Stephen_Canon

I think the operation itself is worth exposing. This is the remainder of a “flooring” division (as opposed to the C-family “truncating” division[1]). If we do provide it, we should also provide the accompanying divide operation.

– Steve

[1] there are several other ways to define division beyond these two: remainder is always positive, remainder is closest to zero, etc. Truncating and flooring division are the most common by a wide margin, however.

@scanon: According to this Wikipedia article, especially the top right diagram, the requested remainder seems to be the one of a euclidean rather than floored division.

Also, from the related recent post I mentioned above:

@Nevin

Neither the % operator nor the quotientAndRemainder(dividingBy:) do what I need in these cases, because they can produce negative remainders. So if I were to suggest something with respect to the ergonomics of integer remainders, it would be to add euclidean division and remainder operations.

Could you please clarify, to make sure we have the correct background for a potential proposal, is it floored or euclidean?