Macro buf_fn

macro_rules! buf_fn {
    ($vis:vis fn $name:ident(&self $(,)? $($arg_name:ident : $arg_ty:ty),*) $(-> $ret:ty)?) => { ... };
    ($vis:vis fn $name:ident(&mut self $(,)? $($arg_name:ident : $arg_ty:ty),*) $(-> $ret:ty)?) => { ... };
}