Macro array 

macro_rules! array {
    () => { ... };
    (=> $cap:literal) => { ... };
    ($elem:expr; $n:expr) => { ... };
    ($elem:expr; $n:expr => $cap:literal) => { ... };
    ($($x:expr),+ $(,)?) => { ... };
    ($($x:expr),+ $(,)? => $cap:literal) => { ... };
}

create an Array.

like vec!, array! has similar syntax as Rust array expressions, with the addition of allowing one to specify the capacity of the Array by appending an =>:

let array = array![1, 2, 3 => 6]; // capacity of 6 elements
assert_eq!(array[0], 1);
assert_eq!(array[1], 2);
assert_eq!(array[2], 3);