Misleading documentation regarding distributions::Uniform

[bgamari]

The first example in the documentation of distributions::Uniform is,

use rand::{NewRng, SmallRng, Rng};
use rand::distributions::Uniform;

let val: f32 = SmallRng::new().sample(Uniform);
println!("f32 from [0,1): {}", val);

The last print directly the earlier discussion of this distribution's semantics; namely that it draws from the open set (0,1).

Moreover, the documentation gives no guidance for users who want the usual half-open uniform distribution drawing from [0,1).

[bgamari]

Presumably one is supposed to use rand::distributions::range::Range for the half-open distribution?

[pitdicker]

Good point. See #392.

[dhardy]

Well spotted.

If there is some specific need for the half-open range it may be worth revisiting our decision to use an open range by default (though maybe more documentation is all that is needed). @bgamari your thoughts on this / reason for wanting a half-open range?

[bgamari]

Indeed, documentation describing the motivation for the open range would be welcome. I'll admit that I found this a bit surprising.

In my case I needed to generate a variate corresponding to an angle, (i.e. on [0, 2*pi)). My first intuition was to scale a standard uniform variate, but after noticing that the standard variate was open I realized I would be better off using a uniform with explicit range.

[dhardy]

If you want to know why see this comment or the whole thread. I'm still uncertain whether this is a good idea myself.

Range::new(0.0, 2.0 * f64::consts::PI) is probably what you want in this case anyway.

[vks]

I believe this was fixed with #392?