pub trait B {
    fn get_sizes<T : Iterator<Item=usize>>(&self) -> T;
    fn handle_sizes<T: Iterator<Item=usize>>(&self) -> T {
        self.get_sizes().filter(|x| x > &2)
    }

    fn transform_size<T : Iterator<Item=usize>> (&self) -> T {
        self.handle_sizes().map(|u| u as u8)
    }
}