use std::mem;

pub trait Split {
    type Buffer;

    fn split(&mut self, usize) -> Option<Self::Buffer>;

    fn fake_split(&mut self) -> Self;
}

impl<'a> Split for &'a [u8] {
    type Buffer = Self;

    fn split(&mut self, n: usize) -> Option<Self::Buffer> {
        if self.len() >= n {
            let (l, r) = mem::replace(self, &[]).split_at(n);
            *self = r;
            Some(l)
        } else {
            None
        }
    }

    fn fake_split(&mut self) -> Self {
        self.split_at(self.len()).0
    }
}
impl<'a> Split for &'a mut [u8] {
    type Buffer = Self;

    fn split(&mut self, n: usize) -> Option<Self::Buffer> {
        if self.len() >= n {
            let (l, r) = mem::replace(self, &mut []).split_at_mut(n);
            *self = r;
            Some(l)
        } else {
            None
        }
    }

    fn fake_split(&mut self) -> Self {
        self.split_at_mut(self.len()).0
    }
}

fn main() {}