`Choose` trait for rand crate

choose.rs

#![feature(specialization)]

extern crate rand;
use rand::Rng;

trait Choose {
    type Item;

    fn choose<R: Rng>(self, rng: &mut R) -> Option<Self::Item>;
}

impl<T: IntoIterator> Choose for T {
    type Item = <T as IntoIterator>::Item;

    default fn choose<R: Rng>(self, rng: &mut R) -> Option<T::Item> {
        let mut value = None;
        for (i, elem) in self.into_iter().enumerate() {
            if i == 0 || rng.gen_range(0, i + 1) == 0 {
                value = Some(elem);
            }
        }
        value
    }
}

impl<'a, T> Choose for &'a [T] {
    fn choose<R: Rng>(self, rng: &mut R) -> Option<&'a T> {
        if self.is_empty() {
            None
        } else {
            Some(&self[rng.gen_range(0, self.len())])
        }
    }
}

impl<'a, T> Choose for &'a mut [T] {
    fn choose<R: Rng>(self, rng: &mut R) -> Option<&'a mut T> {
        if self.is_empty() {
            None
        } else {
            let len = self.len();
            Some(&mut self[rng.gen_range(0, len)])
        }
    }
}

fn main() {
}