fn get_middle<T>(elements: Vec<T>) -> T {
    elements[elements.len() / 2]
}

get_middle(vec![1, 2, 3])

get_middle(vec![1, 2, 3])
// as well as...
get_middle(0..3)

fn get_middle<T, U>(elements: U) -> T
where
    U: IntoIterator<Item = T>,
{
    let _it = elements.into_iter();

    unimplemented!("Do something with `it`");
}

fn main() {
    get_middle(vec![1, 2, 3]);
    get_middle(0..3);
}