Macro typedarray 

macro_rules! typedarray {
    (&in($cx:expr) $($t:tt)*) => { ... };
    (in($cx:expr) let $name:ident : $ty:ident = $init:expr) => { ... };
    (in($cx:expr) let mut $name:ident : $ty:ident = $init:expr) => { ... };
}