Bill Baxter wrote:
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? AndreiI'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
I think that is the primary argument. BUT: * You _can_ still use "[]" in that case.* I also think it'd be worth having a "create a random n-byte number", as well, which would be the main use for a full uint random number. * If you're creating a number in the range 0..uint.max+1, you're going to have to be careful in lots of places. You can't get that number from an array length, for example. * I think that hard-core scientific/mathematical users are the main users of the more esoteric cases, and can be expected to get it right (and have no problem with the "[]","()","(]"... notation. I think that what's important for the default is that be correct and obvious for as many cases as possible.
The strength of "[)" is that if we can say "ALL ranges in D are [) unless otherwise stated by the user", it's hard to ever justify breaking that convention.
