struct Error;

trait WriteBytes<'a> {
    fn write_byte<'b>(&'b mut self, byte: u8) -> Result<(), Error>
    where
        'b: 'a;
}

impl<'a> WriteBytes<'a> for &'a mut [u8] {
    fn write_byte<'b>(&'b mut self, byte: u8) -> Result<(), Error>
    where
        'b: 'a,
    {
        match self.split_first_mut() {
            Some((first, rest)) => {
                *first = byte;
                *self = rest;
                Ok(())
            }
            None => Err(Error),
        }
    }
}

fn main() {
    let mut array = [0, 1, 2, 3, 4];
    let mut buf: &mut [u8] = &mut array;
    buf.write_byte(5);
    println!("{:?}", buf);
}