There is a (very) small argument for unsigned array indexes in C/C++ where indexing is from zero, but as Stefan says, for Julia, with indexing starting at one, you have to test both limits anyway.
On Tuesday, September 22, 2015 at 1:11:03 AM UTC+10, Stefan Karpinski wrote: > > Suppose you have a situation where any UInt value is valid. Since only > valid values can be represented, this implies that you cannot validate > inputs at all – it's impossible to represent any invalid values. So you're > definitely not doing anything useful to catch or report errors. > > Suppose that non-negativity isn't the only criterion for validity. E.g. > array indices: only integral values from 1 to length(v) are valid. That > means you need to check bounds anyway, which means the UInt type doesn't > help at all since you still need to check that the UInt value is ≥ 1 and ≤ > length(v). In fact, using UInt mostly means that you can't easily tell if > you tried to use a value that is too large or too small – arithmetic > wrap-around means you'll almost always get values that are too large. > > Using unsigned integers for error checking is a bogus argument. They hide > errors rather than helping surface or debug them. If you index into an > array and you give an invalid index, you'll get a bounds error. Any type > you build on top of arrays will inherit this checking. If there are > additional constraints that your APIs have on valid inputs, they should > check them. > > On Mon, Sep 21, 2015 at 8:05 AM, Milan Bouchet-Valat <nali...@club.fr > <javascript:>> wrote: > >> Le dimanche 20 septembre 2015 à 17:07 -0400, Jesse Johnson a écrit : >> > In a thread about printing UInt variables, Milan Bouchet-Valat said: >> > > The point is, in Julia using unsigned ints to store values that >> > > should >> > > always be positive is *not* recommended. >> > If that is true, then shouldn't the type be called Byte? It seems the >> > type has been misnamed if it was never intended to store unsigned >> > integers. >> > >> > Further, calling the type UInt is misleading to devs from C lang >> > family >> > who frequently depend on compile-time type checking (ex. int vs. >> > uint) >> > to help ensure no unexpected signs show up. I am not suggesting >> > type-checking is a perfect defense against sign errors, and thorough >> > runtime testing is definitely necessary. In my larger projects >> > combining >> > type checking and runtime tests is almost a practical necessity and >> > can >> > seriously cut down on time spent bug hunting sign errors. >> > >> > That said, I am guessing the suggested solution in Julia is to rely >> > solely on runtime sign checking? I can't see how I could make that >> > practical for my use cases, but it would be good to know if that is >> > what the Julia devs intend. >> I think so. One of the references I could find is this: >> https://groups.google.com/d/msg/julia-users/RX8sFQHvEV4/ttxfYufL7WUJ >> >> >> Regards >> > >
