== Quote from Bill Baxter (wbax...@gmail.com)'s article > On Mon, Feb 16, 2009 at 2:33 AM, Don Clugston <nos...@nospam.com> wrote: > > Andrei Alexandrescu wrote: > >> > >> Don wrote: > >>> > >>> Andrei Alexandrescu wrote: > >>>> > >>>> auto rng = Random(unpredictableSeed); > >>>> auto a = 0.0, b = 1.0; > >>>> auto x1 = uniform!("[]")(rng, a, b); > >>>> auto x2 = uniform!("[)")(rng, a, b); > >>>> auto x3 = uniform!("(]")(rng, a, b); > >>>> auto x4 = uniform!("()")(rng, a, b); > >>> > >>> This is a general issue applying to any numeric range. I've been giving > >>> the issue of numeric ranges some thought, and I have begun an > >>> implementation > >>> of a general abstraction. > >>> Any open range can be converted into a closed range, but the converse > >>> does not apply. So any implementation will be using "[]" internally. > >>> > >>> -range("[)", a, b) == range("(]", -b, -a) > >>> range("[)", a, b) == range("[]", a, predecessor(b)) > >>> range("()", a, b) == range("[]", successor(a), predecessor(b)) > >>> > >>> > >>> There's a couple of difficult situations involving floating-point > >>> numbers. > >>> * "[)" has the uncomfortable property that (-2,-1, rng) includes -2 but > >>> not -1, whereas (1, 2, rng) includes 1 but not 2. > >>> > >>> * any floating point range which includes 0 is difficult, because there > >>> are so many numbers which are almost zero. The probability of getting a > >>> zero > >>> for an 80-bit real is so small that you probably wouldn't encounter it in > >>> your lifetime. I think this weakens arguments based on analogy with the > >>> integer case. > >>> > >>> However, it is much easier to make an unbiased rng for [1,2) than for > >>> [1,2] or (1,2) (since the number of members in the range is even). > >> > >> So what would you recommend? [a, b) for floats and [a, b] for ints, or [a, > >> b) for everything? > >> > >> Andrei > > > > I'm leaning towards [a,b) for everything (consistency with arrays), but I'd > > want to know what the reasoning of the boost/c++0x guys was. > How do you create a random uint that can take on any of uint's values > with [a,b)? That's the main reason I can think of to go with [a,b] > for integral types. With floats it's never useful to use the entire > value range. > --bb
Keep in mind that we're talking only about defaults here. At least in the current implementation, "[)" vs. "[]" can be specified by template parameters. Wanting the entire range of an integer type is an edge case, so it's not important that it be well-supported by the defaults, as long as it can be done without resorting to serious kludges.