On Mon, 2014-09-22 at 11:27 -0700, Jason Ekstrand wrote: > I'm a little unsure. I think trying to completely solve this problem > in a way that will truly make strongly typed languages happy is > insanity. That said, I'm cautiously ok with defining bitfields and > enums as long as we are very careful in scoping what "bitfield" and > "enum" mean. A "bitfield" should have only power of two values and > the result should always be interpreted as an OR of those values. An > enum should have every possible value enumerated. If anyone has a > good example of something that validly doesn't fit into either of > these, please speak up. > > The example of wl_output.transform is an enum because every > possibility is enumerated. From C or a similar language, you can do > fun stuff like "if (transform & WL_OUTPUT_TRANSFORM_FLIPPED)" to > determine if there is a flip. In a strongly typed language, you can't > do this and we shouldn't bend over backwards to make it possible. If > we try and come up with some convoluted system that makes this > possible with typed languages, we're going to cause far more pain than > it's worth. > > > One other thing that we need to keep in mind here is the primary > target audience of Wayland and its libraries. That audience is > compositors and toolkits. Most of those are written in C and C++. > What we don't want to do is to do a bunch of things for the sake of 1% > of the target audience that makes the rest have to bend over > backwards. When I said "cautiously OK", I mean that I don't see that > happening yet and I don't see a valid use for an enum that doesn't > follow one of those two rules. However, if we have a plausible case > where doing so would make everyone's lives easier, I'm going to not be > a big fan. > > > Please note that I'm not trying to insult Haskel or other functional > or strongly typed languages or the people who use them. I'm simply > trying to be pragmatic and recognize that people who want to write an > app in haskel that manually bangs the Wayland protocol isn't the > target audience. > > > --Jason
Completely agree with Jason here. Actually the present "enum" are just mnemotic to 32-bit int or uint values (and that's why the type field in current protocol is "int" or "uint" instead of things like "enum"). Though developers of strongly-typed languages may not like it, it is versatile and makes sense. Any attempt to define what an "enum" or "bitfield" is will change the current semantics and introduce a lot of complexity. There may exist a way to make it work perfectly (and I'm okay with it if it really exists), but I doubt whether the effort worth it since it doesn't do any good to C or C++ wayland programmers, who are the main targeted audience of wayland. Regards, Boyan Ding _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/wayland-devel
