Macro buffer_mut 

macro_rules! buffer_mut {
    () => { ... };
    ($start:tt .. $end:tt) => { ... };
    ($start:tt ..= $end:tt) => { ... };
    ($elem:expr; $n:expr) => { ... };
    ($($x:expr),+ $(,)?) => { ... };
}

A macro for constructing buffers akin to vec![..].