default random object?

[Don Clugston]

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.