A distribution uniformly sampling numbers within a given range.

Uniform is the standard distribution to sample uniformly from a range; e.g. Uniform::new_inclusive(1, 6).unwrap() can sample integers from 1 to 6, like a standard die. Rng::random_range is implemented over Uniform.

Example usage

use rand::Rng;
use rand::distr::Uniform;

let mut rng = rand::rng();
let side = Uniform::new(-10.0, 10.0).unwrap();

// sample between 1 and 10 points
for _ in 0..rng.random_range(1..=10) {
    // sample a point from the square with sides -10 - 10 in two dimensions
    let (x, y) = (rng.sample(side), rng.sample(side));
    println!("Point: {}, {}", x, y);
}

Extending Uniform to support a custom type

To extend Uniform to support your own types, write a back-end which implements the UniformSampler trait, then implement the SampleUniform helper trait to "register" your back-end. See the MyF32 example below.

At a minimum, the back-end needs to store any parameters needed for sampling (e.g. the target range) and implement new, new_inclusive and sample. Those methods should include an assertion to check the range is valid (i.e. low < high). The example below merely wraps another back-end.

The new, new_inclusive, sample_single and sample_single_inclusive functions use arguments of type SampleBorrow<X> to support passing in values by reference or by value. In the implementation of these functions, you can choose to simply use the reference returned by SampleBorrow::borrow, or you can choose to copy or clone the value, whatever is appropriate for your type.

use rand::prelude::*;
use rand::distr::uniform::{Uniform, SampleUniform,
        UniformSampler, UniformFloat, SampleBorrow, Error};

struct MyF32(f32);

#[derive(Clone, Copy, Debug)]
struct UniformMyF32(UniformFloat<f32>);

impl UniformSampler for UniformMyF32 {
    type X = MyF32;

    fn new<B1, B2>(low: B1, high: B2) -> Result<Self, Error>
        where B1: SampleBorrow<Self::X> + Sized,
              B2: SampleBorrow<Self::X> + Sized
    {
        UniformFloat::<f32>::new(low.borrow().0, high.borrow().0).map(UniformMyF32)
    }
    fn new_inclusive<B1, B2>(low: B1, high: B2) -> Result<Self, Error>
        where B1: SampleBorrow<Self::X> + Sized,
              B2: SampleBorrow<Self::X> + Sized
    {
        UniformFloat::<f32>::new_inclusive(low.borrow().0, high.borrow().0).map(UniformMyF32)
    }
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Self::X {
        MyF32(self.0.sample(rng))
    }
}

impl SampleUniform for MyF32 {
    type Sampler = UniformMyF32;
}

let (low, high) = (MyF32(17.0f32), MyF32(22.0f32));
let uniform = Uniform::new(low, high).unwrap();
let x = uniform.sample(&mut rand::rng());