// `core::random`

/// A source of random data
pub trait RandomSource {
    /// Fill `buf` with random bytes.
    /// 
    /// This is the baseline method that must be implemented.
    fn gen_bytes(&mut self, buf: &mut [u8]);

    // Overridable functions for performance.
    // This is similar to the Hasher trait.
    fn gen_u8(&mut self) -> u8;
    fn gen_u16(&mut self) -> u16;
    fn gen_u32(&mut self) -> u32;
    // etc
}

/// A trait for types which can be created from a RandomSource.
pub trait Random {
    fn random(random_source: &mut impl RandomSource) -> Self;
}

// `std::random`

/// Random source that produces cryptographically secure random numbers at a reasonable speed.
///
/// This generator does not encapsulate any state, and cannot be seeded or replayed.
#[derive(Default, Copy, Clone, Debug)]
pub struct DefaultRng;
impl RandomSource for DefaultRng { /* ... */ }

/// Generate a random value
pub fn random<T: Random>() -> T {
    <T as Random>::gen(DefaultRng)
}

Future work:

impl<T> [T] {
    /// Shuffle a slice into a random order
    pub fn shuffle(&mut self);
    
    /// Shuffle a slice into a random order, using the specified random source
    pub fn shuffle_with(&mut self, rng: &mut impl RandomSource);
}

impl Iterator {
    pub fn choose(&mut self)
}

// `std::random`

pub trait RandomSample<T> {
    fn sample() -> T
}

pub fn sample<R: RandomSample<T>>(range: R) -> 

/// Generate a random value in the specified range
pub fn range<T: RandomRange>(bounds: impl RangeBounds<T>) -> T { /* ... */ }

pub fn distribution<T, D: Distribution<T>>(bounds: D) -> T { /* ... */ }
pub fn range<T, D: Distribution<T> + RangeBounds<T>>(bounds: D) -> T { /* ... */ }


// Also a method on RandomSource if you need a specific RNG
pub fn choose<T, D: Distribution<T>>(distribution: D) -> T { /* ... */ }

pub trait Distribution<T> {
    fn sample(&self) -> T {
        self.sample_with(DefaultRng)
    }
    fn sample_with<R: RandomSource + ?Sized>(&self, rng: &mut R) -> T;
}

impl Distribution<i32> for Range<i32> {
    fn sample<R: RandomSource>(&self, rng: &mut R) -> T;
}

impl<'a, T> Distribution<&'a T> for &'a [T] {
    fn sample<R: RandomSource>(&self, rng: &mut R) -> &'a T;
}

impl<T: Clone, N: usize> Distribution<T> for [T; N] {
    fn sample<R: RandomSource>(&self, rng: &mut R) -> T;
}

struct StandardDistribution;
impl Distribution<T: Random> for StandardDistribution {
    fn sample<R: RandomSource + ?Sized>(&self, rng: &mut R) -> T {
        T::gen(rng)
    }
} 

From the rand crate:

pub trait Distribution<T> {
    fn sample<R: RandomSource + ?Sized>(&self, rng: &mut R) -> T;
}