default random object?

[bearophile]

Andrei Alexandrescu:

> 3. How should the global rng be initialized?

Automatically seeded with the time at the beginning of the program. Of course the seed can be set again in any moment.


> 4. While we're at it, should uniform(a, b) generate by default something 
> in [a, b] or [a, b)? Someone once explained to me that generating [a, b] 
> for floating point numbers is the source of all evils and that Hitler, 
> Stalin and Kim Il Sung (should he still be alive) must be using that 
> kind of generator. Conversely, generating [a, b) is guaranteed to bring 
> in the long term everlasting peace to Earth. My problem however is that 
> in the integer realm I always want to generate [a, b]. Furthermore, I 
> wouldn't be happy if the shape of the interval was different for 
> integers and floating point numbers. How to break this conundrum? Don't 
> forget that we're only worrying about defaults, explicit generation is 
> always possible with self-explanatory code:
> 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);

That's awful and ugly. My suggestions are simple (copied from my dlibs and the random std lib of Python):

random() => floating point [0, 1)
randInt(a=0, b) => integral [a, b]
randRange(a=0, b) => integral [a, b)
uniform(a, b) => floating point [a, b)
normal(a, b) => good quality normally-distributed number with given std dev and avg.

Bye,
bearophile